Wound treatment apparatus and method

ABSTRACT

An apparatus for cleansing wounds in which irrigant fluid from a reservoir connected to a conformable wound dressing and wound exudate from the dressing are moved by a device (which may be a single pump or two pumps) for moving fluid through a flow path which passes through the dressing and a means for providing simultaneous aspiration and irrigation of the wound, and means for stressing the wound bed and optionally tissue surrounding the wound. The former removes materials deleterious to wound healing, while distributing materials that are beneficial in promoting wound healing over the wound bed. The latter promotes wound healing. The dressing and a method of treatment using the apparatus.

The present invention relates to apparatus and a medical wound dressingfor aspirating, irrigating and/or cleansing wounds, and a method oftreating wounds using such apparatus for aspirating, irrigating and/orcleansing wounds.

It relates in particular to such an apparatus, wound dressing and methodthat can be easily applied to a wide variety of, but in particularchronic, wounds, to cleanse them of materials that are deleterious towound healing, whilst distributing materials that are beneficial in sometherapeutic aspect, in particular to wound healing.

Aspirating and/or irrigating apparatus are known, and tend to be used toremove wound exudate during wound therapy. In known forms of such woundtherapy, aspiration and irrigation of the wound generally take placesequentially.

Each Part of the Therapy Cycle is Beneficial in Promoting Wound Healing:

Aspiration applies a negative pressure to the wound, which is beneficialin itself in promoting wound healing by removing materials deleteriousto wound healing with the wound exudate, reducing bacterial load,combating peri-wound oedema, increasing local blood flow to the woundand encouraging the formation of wound bed granulation tissue.

Irrigation cleanses wounds of materials that are deleterious to woundhealing by diluting and moving wound exudate (which is typicallyrelatively little fluid and may be of relatively high viscosity andparticulate-filled.

Additionally, relatively little of beneficial materials involved inpromoting wound healing (such as cytokines, enzymes, growth factors,cell matrix components, biological signalling molecules and otherphysiologically active components of the exudate) are present in awound, and are not well distributed in the wound, i.e. they are notnecessarily present in parts of the wound bed where they can bepotentially of most benefit. These may be distributed by irrigation ofthe wound and thus aid in promoting wound healing.

The irrigant may additionally contain materials that are potentially oractually beneficial in respect of wound healing, such as nutrients forwound cells to aid proliferation, and gases, such as oxygen. These maybe distributed by irrigation of the wound and thus aid in promotingwound healing.

If aspiration and irrigation therapy is applied sequentially to a wound,the two therapies, each of which is beneficial in promoting woundhealing, can only be applied intermittently.

Thus, the wound will lose the abovementioned known beneficial effects ofaspiration therapy on wound healing, at least in part, while thataspiration is suspended during irrigation.

Additionally, for a given aspirate flow, whilst materials that arepotentially or actually deleterious in respect of wound healing areremoved from wound exudate, the removal in a given time period ofapplication of the total irrigate and/or aspirate therapy will normallybe less effective and/or slower than with continuous application ofaspiration.

Even less to be desired, is that while aspiration is not applied to thewound, wound exudate and materials deleterious to wound healing (such asbacteria and debris, and iron II and iron III and for chronic woundsproteases, such as serine proteases) will pool on the wound bed andhinder wound healing, especially in a highly exuding wound. The influxof local oedema will also add to the chronicity of the wound. This isespecially the case in chronic wounds.

Depending on the relative volumes of irrigant and wound exudate, themixed exudate-irrigant fluid and may be of relatively high viscosityand/or particulate-filled. Once it is present and has pooled, it may bemore difficult to shift by the application of aspiration in aconventional sequential aspirate—irrigate—dwell cycle than withcontinuous simultaneous aspiration and irrigation of the wound, owing tothe viscosity and blockage in the system.

The wound will also lose the abovementioned beneficial effects ofirrigation therapy on wound healing, at least in part, while thatirrigation is suspended during aspiration.

These benefits in promoting wound healing include the movement ofmaterials that are beneficial in promoting wound healing, such as thosementioned above.

Additionally, for a given irrigant flow, the cleansing of the wound andthe distribution by irrigation of the wound of such beneficial materialsin a given time period of application of the total irrigate and/oraspirate therapy when such therapy is in a conventional sequentialaspirate—irrigate—dwell cycle will normally be less effective and/orslower than with continuous application of aspiration.

Such known forms of aspiration and/or irrigation therapy systems alsooften create a wound environment that may result in the loss of optimumperformance of the body's own tissue healing processes, and slow healingand/or in weak new tissue growth that does not have a strongthree-dimensional structure adhering well to and growing from the woundbed. This is a significant disadvantage, in particular in chronicwounds.

The relevant devices tend not to be portable.

It thus would be desirable to provide a system of aspiration andirrigation therapy for a wound, which

can remove wound exudate and materials deleterious to wound healing fromcontact with the wound bed,whilst simultaneously cleansing it and distributing materials that arebeneficial in promoting wound healing across it.

It is further desirable to provide a system which:

-   a) obviates at least some of the abovementioned disadvantages of    known aspiration and/or irrigation systems, and-   b) is portable.

Vascular supply to, and aspiration in, tissue underlying and surroundingthe wound is often compromised.

It is further desirable to provide a system of therapy that alsopromotes vascular supply to tissue underlying and surrounding a wound,promoting wound healing.

Additionally, known forms of wound dressing and aspiration and/orirrigation therapy systems often create a wound environment under thebacking layer that may result in the loss of optimum performance of thebody's own tissue healing processes, and slow healing and/or in weak newtissue growth that does not have a strong three-dimensional structureadhering well to and growing from the wound bed. This is a significantdisadvantage, in particular in chronic wounds.

It is an object of the present invention to provide a system of therapywhich can:

-   -   i) remove materials deleterious to wound healing from wound        exudate.    -   ii) creates stress or strain across the wound bed and optionally        tissue surrounding the wound, e.g. by applying an optionally        varying positive and/or negative pressure to the wound.

The terms stress and strain have slightly different meanings, but in thecontext of this application, are often used interchangeably. “Stress”refers to a physical force acting upon a surface or structure, in thiscase a wound bed. Stress is typically defined as force per unit area ona surface. “Strain” refers to a mechanical deflection of a surface orstructure caused by stress, again in this case a wound bed. Stress maycause strain, or vice versa, but in the context of the presentapplication, where the term stress is used, it should be understood torefer to stress or strain of the wound bed. For example, applying apositive pressure to a wound bed will apply a stress to the surface ofthe wound bed, but will also apply a strain as the wound bed is aresilient structure which will deflect as a result of the pressure. Onthe other hand deflection of the wound bed in one area (i.e. applying astrain) may cause stress and/or strain in another area. Accordinglywhere the term stress or strain is used in the present application, theyshould not be taken in their strict mechanical meaning (although thatmay be appropriate) but should be understood to mean the deflection orapplication of force to the cells of the wound bed and or surroundingareas.

Such a stress or strain across the wound bed and optionally tissuesurrounding the wound, e.g. an optionally varying positive and/ornegative pressure applied to the wound, has been found to result in anincrease in improvements to wound healing, such as an increase in cellproliferation, revascularisation, improved breaking strength andreduction of wound recurrence.

The resultant tissue growth has a strong three-dimensional structureadhering well to and growing from the wound bed. It also stimulatesblood flow in underlying tissue and optionally tissue surrounding thewound.

Removal of fluid by optionally varying negative pressure leads toreduction of interstitial oedema and pressure directly affecting thelymphatic and capillary system, restoring lymph function.

All of these are beneficial to wound healing.

The application of stress and/or strain to a wound bed to improvehealing is equally applicable to both sequential systems (i.e.empty/fill cycles) or simultaneous irrigate/aspirate systems. Althoughit is generally preferred to use a simultaneous system due to thebenefits of such a system, there may be circumstances where a sequentialsystem is preferred, e.g. due to cost.

According to a first aspect of the present invention there is providedan apparatus for aspirating, irrigating and/or cleansing of a wound,comprising

-   a) a fluid flow path, comprising a conformable wound dressing,    having a backing layer which is capable of forming a relatively    fluid-tight seal or closure over a wound and at least one pipe which    passes through and/or under the wound-facing face to allow    irrigation and/or aspiration of a wound, and wherein the point at    which the at least one pipe passes through and/or under the    wound-facing face forms a relatively fluid-tight seal or closure    over the wound, when in use;-   b) a fluid reservoir connectable by a fluid supply tube to the at    least one pipe and-   c) at least one device for moving fluid through the wound dressing    to the wound and/or moving fluid from the wound; characterised in    that the apparatus it comprises-   d) means for applying stress to the wound bed and optionally tissue    surrounding the wound.

Generally it is preferred that the apparatus has at least one inlet pipefor connection to a fluid supply tube to allow irrigation and

at least one outlet pipe for connection to a fluid offtake tube to allowaspirationeach of which passes through and/or under the wound-facing face.

Such an embodiment is suitable for both sequential and simultaneoussystems, whereas a single pipe system is only suitable for sequentialfill/empty cycles.

In one embodiment the present invention provides means for providingsimultaneous aspiration and irrigation of the wound,

such that fluid may be supplied to fill the flowpath from the fluidreservoir via the fluid supply tube (optionally via means for supplyflow regulation) while fluid is aspirated by a device through the fluidofftake tube (optionally or as necessary via means for aspirate flowregulation).

Such an embodiment is particularly suitable for simultaneous irrigationand aspiration and thus forms a preferred embodiment of the presentinvention.

Where any pipe is described in connection with the apparatus as beingconnected or for connection to a (mating end of a) tube, e.g. a fluidsupply tube or fluid offtake tube, the pipe and the tube may form asingle integer in the flow path.

As noted hereinbefore, the present invention in this aspectadvantageously provides a means for combining more than one therapy in asingle dressing system, such as

-   a) removal of materials deleterious to wound healing from wound    exudate, and-   b) promoting wound healing, by stimulating new tissue growth    adhering well to and growing from the wound bed, by creating stress    across the wound bed and optionally tissue surrounding the wound.

In all relevant embodiments of the present apparatus for irrigating,stressing and/or cleansing wounds, it is advantageous that itadditionally, where appropriate, comprises a system which can regulatethe pressure on the wound bed, under the wound dressing.

Preferably such a system is a conventional automated, programmablesystem which can maintain the wound at or near an appropriate, desiredstress to the wound bed and optionally tissue surrounding the wound, toan appropriate, desired programme while moving fluid over the wound bedat an appropriate, desired rate.

Examples of suitable means for the stimulation of the healing of woundsand tissue adhering well to and growing from the wound bed includeapplying mechanical stimulus to the wound bed and optionally tissuesurrounding the wound via the wound dressing and/or via the fluid underdressing.

Examples of suitable ways in which this can in turn be achieved includeapplying an optionally varying positive and/or negative pressure at anyappropriate point for stressing the wound.

The amplitude of the positive and/or negative pressure on the wound bedand optionally tissue surrounding the wound and/or the fluid thereovermay be constant, but more usually is varied, preferably cyclically,either randomly or regularly. Such cyclical variation of the pressureapplied to the wound is effectively the application of an amplitudewaveform at a desired frequency to apply a desired level of stress tothe wound bed and optionally tissue surrounding the wound (it should benoted that application of a varying pressure may cause strain to thesurface of the wound, i.e. deflection of the wound bed, but this isenvisaged in the term stress as used herein).

The desired level and regime of stress to the wound bed and optionallytissue surrounding the wound may be applied conventionally by varyingthe positive and/or negative pressure applied to the wound bed, e.g. by

-   a) varying the rate of the means for moving fluid over the wound bed    as appropriate or desired, e.g. the rate of any pump used to apply    positive or negative pressure to the wound bed at any appropriate    point for stressing the wound,-   b) bleeding fluids, especially gases, such as air and nitrogen, but    not excluding liquids, such as water and saline, or gas in liquid    aerosols; and gels into the flowpath in any appropriate part of the    apparatus to vary the pressure applied to the wound to a desired    level and/or programme, and/or-   c) varying the pressure in any inflatable filler within the wound    dressing as appropriate or desired, as described in more detail    hereinafter.

Preferably, such regular or random variation of the positive and/ornegative pressure applied to the wound will be effected by conventionalprocess control devices and/or software.

The stimulation of the healing of wounds in the present invention mayalso be effected by agitation of the wound bed and/or creatingintermittent flow and/or turbulence to stimulate the cells. This can bedone preferably by regularly or randomly pulsing a positive and/ornegative pressure applied to the wound at any appropriate point for thispurpose.

Such pulsed variation of the pressure applied to the wound is againeffectively the application of an amplitude waveform at a desiredfrequency to apply a desired level of stress to the wound bed andoptionally tissue surrounding the wound.

Pulsing the pressure on the wound may advantageously also provide ameans to over-ride pain, similar to TENS.

The range of variation of the pulsed positive and/or negative pressureapplied to the wound will be substantially less than the maximum levelsof pressure referred to below, i.e. less than 50% atm and typicallysignificantly lower.

The frequencies of such pulsed stressing across the wound will besubstantially higher than those of the cycles of positive and/ornegative pressure to the wound bed and optionally tissue surrounding thewound for the stimulation of the healing of wounds referred to above.

The range of variation of the pulsed positive and/or negative pressureapplied to the wound will generally be substantially less than themaximum levels of pressure and than the range of variation in the levelsof pressure referred to below in respect of cycles of positive and/ornegative pressure.

To clarify there are two forms of stress generally envisaged as beinguseful, i.e. those achieved by a slow cycling of pressure, and thoseachieved by a more rapid pulsing of pressures. The range of pressure ina “cycle” is typically significantly greater than that of a “pulse”. Ananalogy is a carrier wave (the cycle) containing the pulse superimposedupon it.

Regularly or randomly pulsing any pressure applied to the wound may beeffected essentially as described hereinbefore in connection with thevariation of the positive and/or negative pressure applied to the wound.Again, such regular or random pulsing of the positive and/or negativepressure applied to the wound may be effected by conventional processcontrol devices and/or software.

Such pulsing of any pressure applied to the wound may be applied as anamplitude modulation of the positive and/or negative pressure applied tothe wound bed and optionally tissue surrounding the wound, which in turnmay be held constant, but more usually is varied, preferably cyclically,either randomly or regularly (i.e. the carrier wave referred to abovemay in fact be a constant positive or negative pressure), but this isgenerally less preferred.

Where the levels of such pressure above or below atmospheric are heldconstant, this is often achieved in the present apparatus, whereappropriate, by use of a control device that can regulate the pressurein the wound dressing by bleeding fluids, especially gases, such as airand nitrogen, but not excluding liquids, such as water and saline, orgas in liquid aerosols; and gels into the flowpath in any appropriatepart of the apparatus to vary the pressure applied to the wound to adesired level and/or programme.

This often results in any device for moving fluid through the wound thatis downstream of the dressing and that applies an overall negativepressure in the wound space, e.g. a vacuum pump, pumping a heterogeneousmixture of liquid wound exudate and irrigant from the wound dressingwith bleed gases, such as air and nitrogen. This can result in pulsingof any pressure applied to the wound.

The pumping rate and the dimensions of the offtake and/or supply tubesmay be adjusted to maintain the desired balance of pulsing pressureamplitude and frequencies on the wound.

Preferably such a system is a conventional automated, programmablesystem which can maintain the appropriate pulse regimen to the wound.

Stimulus to the wound bed and optionally tissue surrounding the wound byapplying an optionally varying positive and/or negative pressure andagitation of the wound bed to stimulate the cells by regularly orrandomly pulsing any pressure applied to the wound are mutuallycompatible. They may, as appropriate, be applied alone or together.

Thus, an embodiment of the apparatus for irrigating, stressing and/orcleansing wounds of the present invention is characterised in that itcomprises means for supplying optionally varying positive and/ornegative pressure, which is optionally pulsed, to a wound bed andoptionally tissue surrounding the wound for the stimulation of thehealing of the wound.

As noted hereinbefore, in the present invention in this aspect, thepositive and/or negative pressure on the wound bed and/or the fluidthereover and optionally tissue surrounding the wound may be constant,but more usually is varied, preferably cyclically, either randomly orregularly. Where the pressure on the wound bed and/or the fluidthereover and optionally tissue surrounding is varied, it may be avarying positive or negative pressure, or it may as appropriate varyfrom positive to negative or vice versa, again preferably cyclically,and either randomly or regularly. It may vary about a constant positiveor negative baseline pressure, or less usually about a varying baselinepressure. Examples of maximum levels of such pressure above and belowatmospheric include 50% atm. e.g. between 5 and 40% atm., e.g. between15 and 35% atm.

Examples of suitable frequencies of such regular cycles of pressure forthe stimulation of the healing of wounds include 1 to 48 per 24 hr, suchas 12 to 24 per 24 hr, e.g. 2 to 1 per hr.

Examples of suitable waveforms of such cycles either regularly orrandomly for the stimulation of the healing of wounds include curved,e.g. sinusoidal, random white noise and sawtooth for higher frequencies,and usually square for lower frequencies.

Examples of suitable frequencies of regular pulses for the stimulationof the healing of wounds include 1 to 3000 per min (0.016-50 Hz), e.g.30 to 60 per min, e.g. 3 to 20 per min, i.e. 0.05 to 0.33 Hz, such as 5to 10 per min.

Such pulses may be varying positive or negative pressure pulses, or theymay as appropriate vary from positive to negative or vice versa, againpreferably cyclically, and either randomly or regularly.

They may vary about a constant positive or negative baseline pressure orabout a varying baseline pressure. Examples of maximum amplitudes forsuch pulses are up to 10 mm Hg above and below the constant positive ornegative baseline pressure, e.g. up to 7 mm Hg or up to 3 mm Hg.

Examples of suitable waveforms of such pulses either regularly orrandomly for the stimulation of the healing of wounds include curved,e.g. sinusoidal, random white noise sawtooth, square and asystolic-diastolic asymmetric sawtooth.

Where the amplitude of regular cycles of pressure is modulated bysuperimposed regular pulses for the stimulation of the healing ofwounds, examples of suitable frequencies of the combination includethose where the carrier frequency is 1 to 48 per 24 hours and thesuperimposed frequency of the pressure pulses is 1 to 0.05 Hz, both withthe respective amplitudes noted above.

Examples of suitable waveforms of the cycles and the superimposed pulsesmay be regular or random and include curved, e.g. sinusoidal, randomwhite noise, sawtooth, square and a systolic-diastolic asymmetricsawtooth.

Examples of means for applying an optionally varying positive and/ornegative pressure at any appropriate point for stressing the woundand/or regularly or randomly pulsing any pressure applied to the woundfor promoting wound healing, whether applied alone or together, includea wound dressing as hereinbefore defined that comprises one or moreexpandable and contractible modules capable of applying pressure to thewound bed and optionally tissue surrounding the wound at any appropriatepoint for stressing the wound.

Examples of other suitable means of applying mechanical stimulus to thewound by optionally varying positive and/or negative pressure include amagnetic fluid in a chamber or other hollow structure under the backinglayer of the dressing in contact with the wound bed and/or the fluidthereover. A regularly or randomly (preferably cyclically) varyingand/or pulsing external magnetic field is applied to the magnetic fluid.However, such means are generally less favoured.

Thus, one favoured embodiment of the apparatus for irrigating, stressingand/or cleansing wounds is characterised in that it comprises a wounddressing as hereinbefore defined that comprises one or more expandableand contractible modules. Such a module is capable of applying pressureto the wound bed and optionally tissue surrounding the wound at anyappropriate point for stressing the wound. It should be capable ofmaintaining the pressure on the wound bed and/or the fluid thereover andoptionally tissue surrounding the wound at a constant level, but moreusually it should be capable of regularly or randomly (preferablycyclically) varying and/or pulsing the pressure applied to the wound,all at or near an appropriate, desired level of stress to the wound bedand optionally tissue surrounding the wound, to an appropriate, desiredprogramme while moving fluid over the wound bed at an appropriate,desired rate.

Examples of suitable modules capable of applying pressure to the woundbed at any appropriate point for stressing the wound include a module inthe wound dressing may be made of a polymer that can be electricallystimulated to change shape repeatedly at appropriate frequencies.

A preferred module is a fluid-inflatable body that lies in the wound inuse.

Thus, one favoured embodiment of the apparatus for irrigating, stressingand/or cleansing wounds is characterised in that it comprises a wounddressing as hereinbefore defined that comprises one or morefluid-inflatable modules capable of applying pressure to the wound bedat any appropriate point for stressing the wound.

This is capable of maintaining the pressure on the wound bed and/or thefluid thereover at a constant level, but more usually it is also capableof regularly or randomly (preferably cyclically) varying and/or pulsingthe pressure applied to the wound, all at or near an appropriate,desired level of stress to the wound bed, to an appropriate, desiredprogramme while moving fluid over the wound bed

The module or modules is/are (usually cyclically) inflated and deflatedby admitting and releasing fluid.

Once the inflatable body has been inflated, it may be deflated asappropriate or desired, and then reinflated to again apply a positivepressure to the wound, and the cycle may be repeated as appropriate ordesired.

Alternatively, it may be partially filled with an elastically resilientmaterial, such as an elastomeric foam, that in its rest state is capableof applying a working pressure to the wound bed. The body may then bedeflated as appropriate or desired, and then reinflated under the actionof its filler material to again apply a positive pressure to the wound,and the cycle may be repeated as appropriate or desired.

Examples of forms of the body that are suitable such expandable andcontractible modules capable of applying pressure to the wound bed atany appropriate point for stressing the wound include fluid-inflatablefillers and fluid-inflatable irrigant inlet manifolds comprised in thedressing, as described hereinafter in greater detail.

Where the module is a fluid-inflatable filler, examples of suitablefluids include gases, such as air and nitrogen; liquids, such as waterand saline; gas in liquid aerosols; and gels such as those described ingreater detail hereinafter. Preferred fluids include gases, such as airor nitrogen.

Where the module is a fluid-inflatable irrigant inlet manifold comprisedin the dressing as described hereinafter in greater detail, it will bestimulated to change shape as appropriate and optionally at desiredfrequencies by inflation with irrigant, followed as desired bydeflation.

Examples of Both are Included Hereinafter.

Examples of such fillers include a substantially flat film, sheet ormembrane, defining a chamber, pouch or other structure of the backinglayer, e.g. of polymer film, which can contain the inflation fluid.

It is provided with an inflation device for moving inflation fluid tothe filler, and is connected to it by an inflation tube whichcommunicates with its internal space. The inflation device may alsoserve as a deflation device for moving inflation fluid from the filler,and the inflation tube also serves as a deflation tube.

Alternatively or additionally, where appropriate the filler ashereinbefore defined may have a deflation pipe and a bleed valve towaste, e.g. to a collection bag if a non-gaseous fluid is used. Theinflation device for moving inflation fluid then only serves as aninflation device to apply a positive pressure on the wound bed.

Less usually, the filler may have an inflation device and a deflationdevice.

Where it lies under the backing layer of the wound dressing of theapparatus of the invention, the inflation tube may run to the fillerwithin the wound under the wound-facing face of the wound dressing.

However, the inflation tube may be connected to an inflation pipe thatpasses through the wound-facing face of the backing layer, the point atwhich the inflation pipe passes through the wound-facing face forming arelatively fluid-tight seal.

The inflation pipe may be in the form of an aperture, such as a funnelhole, opening, orifice, luer, slot or port for connection as a femalemember respectively to a mating end of the inflation tube (optionally oras necessary via means for forming a tube, pipe or hose, or nozzle).

Where the pipe passes through, rather than under the backing layer, thebacking layer may often have a rigid and/or resiliently inflexible orstiff area to resist any substantial play between the or each pipe andthe or each mating tube, or deformation under pressure in any direction.

It may often be stiffened, reinforced or otherwise strengthened by aboss projecting distally (outwardly from the wound) around each relevanttube, pipe or hose, or nozzle, hole, opening, orifice, luer, slot orport for connection to a mating end of the inflation tube.

The components may be a push, snap or twist-lock fit with each other.

The minimum calibre of the inflation tube and pipe must be sufficientfor them to permit as rapid inflation and deflation of the filler as isdesired.

Suitably the range of cross-dimensions of the bore (i.e. calibre) may be0.5 to 6 mm, e.g. 1.5 to 2 mm.

Each should be resiliently flexible, and preferably soft with goodconformability. This can be done for example by forming it of a suitablematerial, e.g. a resilient thermoplastic.

Examples of suitable inflation device for moving fluid into the fillerinclude pumps. As noted above, the inflation device may also serve as adeflation device for moving inflation fluid from the filler, and theinflation tube also serves as a deflation tube. In such case, the pumpmust be a reversible pump used to increase and decrease the pressure onthe wound bed as desired.

Subject to this consideration, the type and/or capacity of the devicewill also be largely determined by

the appropriate or desired positive or negative pressure to the woundbed, the nature of the fluid, i.e. whether it is a gas, such as air andnitrogen; a liquid, such as water and saline; a gas in liquid aerosol;or a gel;the desired frequencies and waveforms of such cycles either regularly orrandomly.

The following types of pump may be used to apply positive pressure, asdesired to the filler through an inflation tube which communicates withits internal space:

Reciprocating Pumps, such as:

-   Syringe or piston pumps—providing high pressure and high accuracy;-   Diaphragm pumps—where pulsations of one or two flexible diaphragms    displace liquid while check valves control the direction of the    fluid flow e.g. preferably a small portable diaphragm pump.    and    Rotary pumps, such as:-   Centrifugal pumps—with rotating vaned disk attached to a drive shaft    moving fluid without pulsation as it spins. The outlet can be    restricted without damaging the pump.-   Peristaltic pumps—with rollers on a rotor acting on fluid in a tube,    e.g. preferably a small portable peristaltic pump.

Of these, only piston pumps and rotary pumps, such as centrifugal pumpsand peristaltic pumps are readily reversible pumps that may be used toincrease and decrease the pressure on the wound bed as desired.

Subject to this consideration, preferred reversible pumps include asmall portable peristaltic pump.

Preferred non-reversible pumps to be used with a bleed valve to thefiller then include a small portable syringe pump (which is often usedonce and then disposed of) or small portable diaphragm pump, e.g. asphygmometric pump.

Where the module is a fluid-inflatable irrigant inlet manifold comprisedin the dressing as described herein after in greater detail, it will bestimulated to change shape as appropriate and optionally at desiredfrequencies by inflation with irrigant, followed as desired by partialdeflation. It should be noted that the use of such a system is moresuited to a simultaneous system but could be applied to a sequential(i.e. fill/empty cycle) system. When the manifold is inflated it willinfluence the pressure applied to the surface of the wound, and whendeflated the pressure will be reduced (i.e. relative to the baseline ofthe system).

The device for moving fluid through the wound is used to move irrigantto inflate the inlet manifold and apply a positive pressure to the woundbed. As noted hereinafter, the device may suitably be a pump.

As noted hereinbefore, the pressure on the wound bed may be constant,but may be varied, preferably cyclically, either randomly or regularly.

To achieve this, the present apparatus, where appropriate, comprises asystem that can regulate the pump output to the inlet manifold in thewound dressing.

Preferably such a system is a conventional automated, programmablesystem which can maintain the wound at or near an appropriate, desiredflow stress to the wound bed to an appropriate, desired programme whilemoving fluid over the wound bed.

As noted hereinbefore, stimulation of the healing of wounds in thepresent invention may also be effected by regularly or randomly pulsinga pressure applied to the wound at any appropriate point for thispurpose.

Such pulsed flow across the wound may be provided by some types of thedevice for moving fluid through the wound. Certain diaphragm pumpsdescribed hereinafter in greater detail will be appropriate for thispurpose, as are certain peristaltic pumps, and an electromechanicaloscillator directly coupled to the wound dressing, would also besuitable.

Suitable materials for such modules (i.e. fillers, manifolds etc) of anytype include synthetic polymeric materials that do not absorb aqueousfluids, such as polyolefins, polysiloxanes and polyesters. They may behydrophilic, and thus also include hydrophilic polyurethanes. They alsoinclude thermoplastic elastomers and elastomer blends, for examplecopolymers, such as ethyl vinyl acetate polystyrene and elastomericpolyurethane formed by solution casting.

Where the present invention involves simultaneous irrigation/aspirationit provides several further advantages.

One is that application of an irrigant to a wound under simultaneousaspiration creates a wound environment that is exposed to the continuousbeneficial effects of both aspects of the therapy for wound healing, asopposed to the sequential intermittent application of irrigant flow andaspiration in known aspirating and/or irrigating apparatus. The latterresult in less than optimum performance of the body's own tissue healingprocesses, and slower healing and/or weaker tissue growth that does nothave a strong three-dimensional structure adhering well to and growingfrom the wound bed. This is a significant disadvantage, in particular inchronic wounds.

Such a system is particularly suited for removing materials deleteriousto wound healing with the wound exudate, reducing bacterial load,combating peri-wound oedema and encouraging the formation of wound bedgranulation tissue.

Preferred embodiments of the apparatus of the present invention foraspirating, irrigating and/or cleansing chronic wounds apply a mildernegative pressure than in conventional negative pressure therapy (whichis too aggressive for the fragile tissues of many such wounds). Thisleads to increased patient comfort, and lessens the risk of inflammationof the wound.

The removal of wound exudate in a given time period of application ofthe simultaneous irrigate and/or aspirate therapy will normally be moreeffective and/or faster than with a conventional sequential intermittentaspiration and/or irrigation therapy.

Even more desirably, since simultaneous aspiration and irrigation isapplied to the wound, wound exudate and materials deleterious to woundhealing (such as bacteria and debris, and iron II and iron III and forchronic wounds proteases) will not pool on the wound bed and hinderwound healing, especially in a highly exuding wound. This is especiallyimportant in chronic wounds.

The resulting mixed exudate-irrigant fluid will usually be of relativelylower viscosity.

Because simultaneous aspiration and irrigation of the wound providescontinuous removal at a constant relatively high speed, the fluid doesnot have to be accelerated cyclically from rest, and will be easier toshift than with known forms of aspiration and/or irrigation therapysystems with a conventional sequential aspirate—irrigate—dwell cycle.This will thus exert a greater net effect on the removal of adherentbacteria and debris.

This is especially the case in those embodiments of the apparatus of thepresent invention for aspirating, irrigating and/or cleansing woundswhere there is an inlet manifold (as described below).

An inlet manifold generally covers and contacts a significant area,preferably most, of the wound bed with openings that deliver the fluiddirectly to the wound bed over an extended area.

It will be seen that the balance of fluid between fluid aspirated fromthe wound and irrigant supplied to the wound from the irrigant reservoirmay provide a predetermined steady state concentration equilibrium ofmaterials beneficial in promoting wound healing over the wound bed.Simultaneous aspiration of wound fluid and irrigation at a controlledflow rate aids in the attainment and maintenance of this equilibrium

The apparatus for irrigating and/or aspirating wounds of the presentinvention may be used cyclically and/or with reversal of flow.

Preferably the present apparatus for aspirating, irrigating and/orcleansing wounds is a conventionally automated, programmable systemwhich can cleanse the wound with minimal supervision.

The means for providing simultaneous aspiration and irrigation of thewound often comprise:

-   -   a (first) device for moving fluid through the wound applied to        fluid downstream of and away from the wound dressing, in        combination with at least one of    -   a second device for moving fluid through the wound applied to        the irrigant in the fluid supply tube upstream of and towards        the wound dressing;        means for aspirate flow regulation, connected to a fluid offtake        tube; and        means for supply flow regulation, connected to a fluid supply        tube.

The (first) device will generally apply negative pressure (i.e.below-atmospheric pressure or vacuum) to the wound bed. It may beapplied to the aspirate in the fluid offtake tube downstream of and awayfrom the wound dressing.

Alternatively or additionally, where appropriate, the aspirate in thefluid offtake tube downstream of the wound dressing may be aspiratedinto a collection vessel, and the first device may act on fluid such asair from the collection vessel. This prevents contact of the device withthe aspirate.

The (first) device may be a fixed-throughput device, such as afixed-speed pump, which will usually require a discrete means foraspirate flow regulation, connected to a fluid offtake tube, and/ormeans for supply flow regulation, connected to a fluid supply tube, ineach case, e.g. a regulator, such as a rotary valve.

Alternatively, where appropriate the (first) device for moving fluidthrough the wound may be a variable-throughput device, such as avariable-speed pump, downstream of the wound dressing, thus effectivelyforming a combination of a (first) device for moving fluid through thewound with means for aspirate flow regulation and/or means for supplyflow regulation in a single integer.

The (first) device for moving fluid through the wound will often be apump of any of the types set out below, or a piped supply of vacuum,applied to fluid downstream of and away from the wound dressing.

The Following Types of Pump May be Used as the (First) Device:

Reciprocating Pumps, such as:

-   Piston Pumps—where pistons pump fluids through check valves, in    particular for positive and/or negative pressure on the wound bed;    and-   Diaphragm Pumps—where pulsations of one or two flexible diaphragms    displace liquid with check valves.    and    Rotary Pumps, such as:-   Progressing cavity pumps—with a cooperating screw rotor and stator,    in particular for higher-viscosity and particulate-filled exudate;    and-   Vacuum pumps—with pressure regulators.

The (first) device may be a diaphragm pump, e.g. preferably a smallportable diaphragm pump. This is a preferred type of pump, in order inparticular to reduce or eliminate contact of internal surfaces andmoving parts of the pump with (chronic) wound exudate, and for ease ofcleaning.

Where the pump is a diaphragm pump, the one or two flexible diaphragmsthat displace liquid may each be, for example a polymer film, sheet ormembrane, that is connected to means for creating the pulsations. Thismay be provided in any form that is convenient, inter alia as apiezoelectric transducer, a core of a solenoid or a ferromagneticinteger and coil in which the direction of current flow alternates, arotary cam and follower, and so on.

Where any second device is applied to the fluid in the fluid supply tubeupstream of and towards the wound dressing, it will usually applypositive pressure (i.e. above-atmospheric pressure) to the wound bed.

As with the (first) device, it may be a fixed-throughput device, such asa fixed-speed pump, which will usually require a discrete means forsupply flow regulation, connected to a fluid supply tube, e.g. aregulator, such as a rotary valve.

Alternatively, where appropriate the second device for moving irrigantfluid to the wound may be a variable-throughput device, such as avariable-speed pump, upstream of the wound dressing, thus effectivelyforming a combination of a second device for moving fluid through thewound with means for supply flow regulation in a single integer.

The second device for moving fluid through the wound will often be apump of any of the following types applied to the irrigant in the fluidsupply tube upstream of and towards the wound dressing. It may be afixed-speed pump, with (as above) a discrete means for supply flowregulation, connected to a fluid supply tube, e.g. a regulator, such asa rotary valve. Alternatively, where appropriate the pump may be avariable-throughput or variable-speed pump.

The Following Types of Pump May be Used as the Second Device:

Reciprocating Pumps, such as:

-   Shuttle Pumps—with an oscillating shuttle mechanism to move fluids    at rates from 2 to 50 ml per minute    and    Rotary Pumps, such as:-   Centrifugal pumps Flexible impeller pumps—where elastomeric impeller    traps fluid between impeller blades and a moulded housing that    sweeps fluid through the pump housing.-   Peristaltic pumps—with peripheral rollers on rotor arms acting on a    flexible fluid aspiration tube to urge fluid current flow in the    tube in the direction of the rotor.-   Rotary vane pumps—with rotating vaned disk attached to a drive shaft    moving fluid without pulsation as it spins. The outlet can be    restricted without damaging the pump.

The second device may be a peristaltic pump, e.g. preferably a smallportable peristaltic pump. This is a preferred type of pump, in order inparticular to reduce or eliminate contact of internal surfaces andmoving parts of the pump with irrigant, and for ease of cleaning.

Where the pump is a peristaltic pump, this may be e.g. an Instech ModelP720 miniature peristaltic pump, with a flow rate: of 0.2-180 ml/hr anda weight of <0.5 k. This is potentially useful for home and fieldhospital use.

Each such pump of any these types may also suitably be one that iscapable of pulsed, continuous, variable and/or automated and/orprogrammable fluid movement. Less usually and less preferably, each suchpump of any these types will be reversible.

As above, the means for supply flow regulation may be a regulator, suchas a rotary valve. This is connected between two parts of a fluid supplytube, such that the desired supply flow regulation is achieved.

If there are two or more inlet pipes, these may be connected to a singlefluid supply tube with a single regulator, or to first, second, etc.fluid supply tubes, respectively having a first regulator, a secondregulator, etc., e.g. a valve or other control device for admittingfluids into the wound.

As above, the means for aspirate flow regulation may be similarlyprovided in a form in which concomitant aspirate flow regulation ispossible. It may be a regulator, such as a valve or other controldevice, e.g. a rotary valve.

Multiple offtake tubes may be similarly provided with single or multipleregulators, all for aspiration of fluids from the apparatus, e.g. to aaspirate collection vessel, such as a collection bag.

If there is no second device for moving fluid through the wound appliedto the irrigant in the fluid supply tube upstream of and towards thewound dressing, it is only possible to apply a negative pressure to thewound, by means of the device for moving fluid through the wound appliedto the aspirate in the fluid offtake tube downstream of and away fromthe wound dressing.

Operation may e.g. be carried out at a negative pressure of up to 50%atm., typically at a low negative pressure of up to 20% atm., moreusually up to 10% atm. at the wound, as is described hereinafter.

Examples of suitable and preferred (first) devices include as describedhereinbefore, a diaphragm pump, e.g. preferably a small portablediaphragm pump. This is a preferred type of pump, in order in particularto reduce or eliminate contact of internal surfaces and moving parts ofthe pump with (chronic) wound exudate, and for ease of cleaning.

Alternatively, if it is desired to apply a net positive pressure to thewound, the means for providing simultaneous aspiration and irrigation ofthe wound must comprise not only

-   -   a first device for moving fluid through the wound applied to the        aspirate in the fluid offtake tube downstream of and away from        the wound dressing, but also    -   a second device for moving fluid through the wound applied to        the irrigant in the fluid supply tube upstream of and towards        the wound dressing.

Operation may then e.g. be carried out at a positive pressure of up to50% atm., typically at a low positive pressure of up to 20% atm., moreusually up to 10% atm. at the wound, as is described hereinafter.

Examples of suitable and preferred first devices include those types ofpump that are so described hereinbefore in relation to the first device.This may be a diaphragm pump, e.g. preferably a small portable diaphragmpump.

Examples of suitable and preferred second devices include those types ofpump that are so described hereinbefore in relation to the first device.This may be a peristaltic pump, e.g. a miniature peristaltic pump.

It is of course equally possible to apply a negative pressure to thewound, by means of such a combination of;

-   -   a first device for moving fluid through the wound applied to the        aspirate in the fluid offtake tube downstream of and away from        the wound dressing, and    -   a second device for moving fluid through the wound applied to        the irrigant in the fluid supply tube upstream of and towards        the wound dressing;        optionally with    -   means for supply flow regulation, connected to a fluid supply        tube; and/or    -   means for aspirate flow regulation, connected to a fluid offtake        tube.

Indeed, as noted below in this regard, preferred embodiments of theapparatus of this first aspect of the present invention for aspirating,irrigating and/or cleansing chronic wounds that apply a negativepressure include such types of combination of;

-   -   a first device, e.g. a diaphragm pump, e.g. preferably a small        portable diaphragm pump, and    -   a second device, e.g. a peristaltic pump, preferably a miniature        peristaltic pump.

As noted above, either of the first device and the second device may bea fixed-throughput device, such as a fixed-speed pump, which willusually require a discrete means for aspirate flow regulation, connectedto a fluid offtake tube, and/or means for supply flow regulation,connected to a fluid supply tube, in each case, e.g. a regulator, suchas a rotary valve, or a variable-throughput device, such as avariable-speed pump, downstream of the wound dressing, thus effectivelyforming a combination of a (first) device for moving fluid through thewound with means for aspirate flow regulation and/or means for supplyflow regulation in a single integer.

The higher end of the ranges of % positive and negative pressure notedabove are potentially more suitable for hospital use, where they mayonly be used safely under professional supervision. The lower end ispotentially more suitable for home use, where relatively high % positiveand negative pressures cannot be used safely without professionalsupervision, or for field hospital use.

In each case, the pressure on the wound may be held constant throughoutthe desired length of therapy, or may be varied cyclically in a desiredpositive or negative pressure regime.

As noted above, when it is desired to apply a negative pressure to thewound, it is preferred that the means for providing simultaneousaspiration and irrigation of the wound comprise not only

-   -   a (first) device for moving fluid through the wound applied to        the aspirate in the fluid offtake tube downstream of and away        from the wound dressing, but also    -   a second device for moving fluid through the wound applied to        the irrigant in the fluid supply tube upstream of and towards        the wound dressing.

Accordingly, one embodiment of the apparatus for irrigating, cleansingand/or aspirating wounds of the present invention is characterised inthe means for providing simultaneous aspiration and irrigation of thewound comprises:

-   -   a (first) device for moving fluid through the wound applied to        fluid downstream of and away from the wound dressing, and    -   a second device for moving fluid through the wound applied to        the irrigant in the fluid supply tube upstream of and towards        the wound dressing, and        in combination with at least one of    -   means for supply flow regulation, connected to a fluid supply        tube, and    -   means for aspirate flow regulation, connected to a fluid offtake        tube.

As noted above, either of the first device and the second device may bea fixed-throughput device, such as a fixed-speed pump, which willusually require a discrete means for aspirate flow regulation, connectedto a fluid offtake tube, and/or means for supply flow regulation,connected to a fluid supply tube, in each case, e.g. a regulator, suchas a rotary valve, or

a variable-throughput device, such as a variable-speed pump, downstreamof the wound dressing, thus effectively forming a combination of a(first) device for moving fluid through the wound with means foraspirate flow regulation and/or means for supply flow regulation in asingle integer.

This combination of

-   -   a device for moving fluid through the wound applied to the        aspirate in the fluid offtake tube downstream of and away from        the wound dressing,        and    -   a device for moving fluid through the wound applied to the fluid        in the fluid supply tube upstream of and towards the wound        dressing, may be used to apply an overall positive or negative,        or even zero pressure to the wound.

At least one body in the flow path to, over and from the wound bedshould have sufficient resilience against the pressure to allow anysignificant compression or decompression of the fluid occur.

Thus, examples of suitable bodies include those which are or are definedby a film, sheet or membrane, such as inlet or offtake and/or tubes andstructures such as bags, chambers and pouches, filled with irrigantfluid, and e.g. the backing layer of the wound dressing, made ofelastically resilient thermoplastic materials.

It will be seen that the balance of fluid between aspirated fluid fromthe wound and irrigant supplied to the wound from the fluid reservoirwill thus be largely determined by a means for providing simultaneousaspiration and irrigation of the wound which may be a system comprising:

-   a) means for aspirate flow regulation and/or a device for moving    fluid through the wound applied to fluid downstream of and away from    the wound dressing, and-   b) means for supply flow regulation and/or a device for moving fluid    through the wound applied to the fluid in the fluid supply tube    upstream of and towards the wound dressing.

The same means may be used to apply an overall positive or negative, oreven neutral pressure to the wound. The means may also be used to varythe pressure in the wound dressing (e.g. via a manifold) to apply stressto the wound bed and optionally areas surrounding the wound.

The appropriate flow rate through the supply tube will depend on anumber of factors, such as:

-   -   the viscosity and consistency of each of the irrigant, exudate        and mixed exudate-irrigant fluid, and any changes as the wound        heals;    -   the level of negative pressure on the wound bed;    -   whether the irrigant in the fluid supply tube upstream of and        into the wound dressing is under positive pressure, and the        level of such pressure;    -   the level of any pressure drop between the irrigant in the fluid        supply tube upstream of the wound dressing and the wound bed,        such as across a porous element, e.g. a membrane wound contact        layer on the lower surface of an inlet manifold that delivers        the fluid directly to the wound bed;    -   the depth and/or capacity of the wound; and    -   the power consumption needed for a given desired fluid volume        flow rate of irrigant and/or wound exudate through the wound.

The dressing may comprise an inlet manifold (as described in furtherdetail hereinafter) that covers and contacts a significant area,preferably most, of the wound bed with openings that deliver the fluiddirectly to the wound bed over an extended area, in the form of one ormore inflatable hollow bodies defined by a film sheet or membrane. Ingeneral a manifold will cover 50% of the wound preferably 75% or more,though it is possible that it may cover a smaller area of the wound.

The (usually small) positive pressure above atmospheric from theirrigation device when both devices are running together should besufficient to inflate the manifold.

The desired fluid volume flow rate of irrigant and/or wound exudate ispreferably that for optimum performance of the wound healing process.

The flow rate will usually be in the range of 1 to 1500 ml/hr, such as 5to 1000 ml/hr, e.g. 15 to 300 ml/hr, such as 35 to 200 ml/hr through thesupply tube. The flow rate through the wound may be held constantthroughout the desired length of therapy, or may be varied cyclically ina desired flow rate regime.

In practice, the offtake rate of flow of total irrigant and/or woundexudate will generally be of the order of 1 to 2000, e.g. 35 to 300ml/24 hr/cm², where the cm² refers to the wound area, depending onwhether the wound is in a highly exuding state.

In practice, the rate of exudate flow is typically only of the order ofup to 75 microlitres/cm²/hr (where cm² refers to the wound area), andthe fluid can be highly mobile or not, depending on the level ofproteases present). Exudate levels drop and consistency changes as thewound heals, e.g. to a level for the same wound that equates to 12.5-25microlitres/cm²/hr.

It will be apparent that the aspirated fluid from the wound willtypically contain a preponderance of irrigant from the fluid reservoirover wound exudate.

The necessary adjustments to maintain the desired balance of fluid bymeans of

-   a) the means for aspirate flow regulation and/or downstream device,    and-   b) the means for supply flow regulation and/or upstream device for    moving fluid    will be apparent to the skilled person, bearing in mind that, as    noted above, either of the first device and the second device may    be:    -   a fixed-throughput device, such as a fixed-speed pump, which        will usually require a discrete means for aspirate flow        regulation, connected to a fluid offtake tube, and/or means for        supply flow regulation, connected to a fluid supply tube, in        each case, e.g. a regulator, such as a rotary valve, or    -   a variable-throughput device, such as a variable-speed pump,        downstream of the wound dressing, thus effectively forming a        combination of a (first) device for moving fluid through the        wound with means for aspirate flow regulation and/or means for        supply flow regulation in a single integer.

The type and/or capacity of a suitable first and/or second device willbe largely determined by

-   a) the appropriate or desired fluid volume flow rate of irrigant    and/or wound exudate from the wound, and-   b) whether it is appropriate or desired to apply a positive or    negative pressure to the wound bed, and the level of such pressure    to the wound bed for optimum performance of the wound healing    process, and-   c) by factors such as portability, power consumption and isolation    from contamination.

As noted above, when it is desired to apply a negative pressure to thewound with the apparatus of the present invention for aspirating,irrigating and/or cleansing wounds to provide simultaneous aspirationand irrigation of the wound, the means for providing simultaneousaspiration and irrigation of the wound may comprise

-   -   a single device for moving fluid through the wound applied to        the aspirate in the fluid offtake tube downstream of and away        from the wound dressing or in combination with at least one of:    -   means for supply flow regulation, connected to a fluid supply        tube, and    -   means for aspirate flow regulation, connected to a fluid offtake        tube.

As noted above, the device may be a fixed-throughput device or avariable-throughput device.

In a further aspect the present invention provides a method of operationof an apparatus for aspirating, irrigating and/or cleansing wounds saidmethod comprising the steps of:

-   a) providing an apparatus as set out above;-   b) applying the wound dressing to the wound;-   c) conforming the backing layer of the wound dressing to the shape    of the bodily part in which the wound is to form a relatively fluid    tight seal or closure;-   d) activating the at least one device for moving fluid through the    wound dressing to the wound and/or from the wound to cause irrigant    to move to the wound; and-   e) activating the means for stressing the wound bed and optionally    tissue surrounding the wound to apply a stress to the wound bed.

In a preferred embodiment the apparatus has at least one inlet pipe andat least one outlet pipe, each of which passes through and/or under thewound-facing face. Such an embodiment allows for a method simultaneousand/or sequential irrigation/aspiration of the wound. In such anembodiment step d) of the method comprises activating the at least onedevice of moving fluid through the wound dressing to move fluid(irrigant) through the at least one inlet and to move fluid (aspirate)out of the at least one outlet pipe.

In a preferred embodiment the irrigant is moved to the wound via theinlet pipe and aspirate removed from the outlet pipe simultaneously,i.e. simultaneous irrigation/aspiration. This may be carried out forsubstantially the entirety of the treatment of the wound, or alternatelyfor portions of the treatment as desired.

Such an embodiment is also suitable for sequential (fill/empty)operation, and thus a method wherein sequential operation is carried outforms an alternative embodiment of the invention. In such an embodimentirrigation would be ceased by ceasing the device moving fluid throughthe at least one inlet and activating a device to move fluid from thewound through the outlet.

Suitable flow rates, parameters for operation of the means for applyingstress and for operation of the apparatus in general are set out above.Further details are given below.

The operation of a typical apparatus of this type for simultaneousaspiration and irrigation of a wound at a low negative pressure of up to20% atm., more usually up to 10% atm. at the wound, with one pump mayinvolve the following steps. As mentioned previously, the application ofnegative pressure has beneficial effects in wound healing.

Before starting the apparatus of this first aspect of the presentinvention for aspirating, irrigating and/or cleansing wounds, thebacking layer of the wound dressing is applied over the wound andconformed to the shape of the bodily part in which the wound is to forma relatively fluid-tight seal or closure.

The means for supply flow regulation, connected to a fluid supply tube,such as a regulator, such as a rotary valve, is usually closed, and themeans for aspirate flow regulation (if any), connected to a fluidofftake tube, is opened.

The aspiration pump (i.e. first device) is started and run to give anegative pressure of up to 50% atm., more usually up to 20% atm., e.g.up to 10% atm. to be applied to the interior of the dressing and thewound.

The means for fluid supply regulation is opened and is then adjusted,and/or where the aspiration pump is a variable-speed pump, downstream ofthe wound dressing, that is adjusted, to maintain the desired balance offluid at a controlled nominal flow rate and to maintain the desirednegative pressure in the interior of the wound dressing.

The means of applying stress is then activated. Typically the means forapplying stress comprises at least one expandable or contractible modulecapable of applying pressure to the wound bed. In one embodiment such amodule comprises an inflatable body which lies within the wound in use.The inflatable body may be used to apply a constant pressure (and hencestress) to the wound or, preferably, may be used to apply a cyclicalpressure. The module may be inflated and deflated be introducing andremoving fluid to the body. Further details of suitable modules andtheir operation are given above.

The apparatus is then run for the desired length of therapy and with thedesired negative pressure and stress regime. After this period, theaspiration pump is stopped.

The operation of a typical apparatus for simultaneous aspiration andirrigation of a wound at a low negative pressure of up to 20% atm., moreusually up to 10% atm. at the wound, with two pumps may involve thefollowing steps.

The necessary changes where the mode of operation for a net positivepressure of e.g. up to 15% atm., more usually up to 10% atm. at thewound will be apparent to the skilled person.

A typical apparatus for simultaneous aspiration and irrigation of awound at a low negative pressure of up to 20% atm., more usually up to10% atm. at the wound comprises means for providing simultaneousaspiration and irrigation of the wound which is a combination of

-   a) a first device for moving fluid through the wound applied to the    aspirate in the fluid offtake tube downstream of and away from the    wound dressing, with optional means for aspirate flow regulation,    connected to a fluid offtake tube: and-   b) a second device for moving fluid through the wound applied to the    irrigant in the fluid supply tube upstream of and towards the wound    dressing, with optional means for supply flow regulation, connected    to a fluid supply tube.

As noted above, either device may be a fixed-throughput device or avariable-throughput device.

Before starting the apparatus of this first aspect of the presentinvention for aspirating, irrigating and/or cleansing wounds, thebacking layer of the wound dressing is applied over the wound andconformed to the shape of the bodily part in which the wound is to forma relatively fluid-tight seal or closure.

Any means for supply flow regulation, connected to a fluid supply tube,such as a regulator, such as a rotary valve, is usually closed, and anymeans for aspirate flow regulation, connected to a fluid offtake tube,is opened.

The aspiration pump is started and run to apply a negative pressure ofup to 50% atm., more usually up to 20% atm., e.g. up to 10% atm., to theinterior of the dressing and the wound.

The irrigation pump is then started, so that both pumps are runningtogether, and any means for supply flow regulation is opened.

The irrigation pump flow rate and any means for fluid supply regulationare then adjusted and/or where the aspiration pump and/or the irrigationpump is a variable-speed pump, either or both is/are is adjusted, tomaintain the desired balance of fluid at a controlled nominal flow rateand to maintain the desired negative pressure in the interior of thewound dressing.

The means for applying stress is then activated, as described above.

The apparatus is then run for the desired length of therapy and with thedesired pressure regime. After this period, the irrigation pump isstopped, shortly followed by the aspiration pump.

In all embodiments of the apparatus of the present invention foraspirating, irrigating and/or cleansing wounds, a particular advantageis the tendency of the wound dressing to conform to the shape of thebodily part to which it is applied.

The term ‘relatively fluid-tight seal or closure’ is used herein toindicate one which is fluid- and microbe-impermeable and permits apositive or negative pressure of up to 50% atm., more usually up to 20%atm., e.g. up to 10% atm. to be applied to the wound. The term ‘fluid’is used herein to include gels, e.g. thick exudate, liquids, e.g. water,and gases, such as air, nitrogen, etc.

The shape of the backing layer that is applied may be any that isappropriate to aspirating, irrigating and/or cleansing the wound acrossthe area of the wound.

Examples of such include a substantially flat film, sheet or membrane,or a bag, chamber, pouch or other structure of the backing layer, e.g.of polymer film, which can contain the fluid.

The backing layer may be a film, sheet or membrane, often with a(generally uniform) thickness of up to 100 micron, preferably up to 50micron, more preferably up to 25 micron, and of 10 micron minimumthickness.

Its largest cross-dimension may be up to 500 mm (for example for largetorso wounds), up to 100 mm (for example for axillary and inguinalwounds), and up to 200 mm for limb wounds (for example for chronicwounds, such as venous leg ulcers and diabetic foot ulcers.

Desirably the dressing is resiliently deformable, since this may resultin increased patient comfort, and lessen the risk of inflammation of awound. Suitable materials for it include synthetic polymeric materialsthat do not absorb aqueous fluids, such as polyolefins, such aspolyethylene e.g. high-density polyethylene, polypropylene, copolymersthereof, for example with vinyl acetate and polyvinyl alcohol, andmixtures thereof; polysiloxanes; polyesters, such as polycarbonates;polyamides, e.g. 6-6 and 6-10, and hydrophobic polyurethanes.

They may be hydrophilic, and thus also include hydrophilicpolyurethanes.

They also include thermoplastic elastomers and elastomer blends, forexample copolymers, such as ethyl vinyl acetate, optionally or asnecessary blended with high-impact polystyrene.

They further include elastomeric polyurethane, particularly polyurethaneformed by solution casting.

Preferred materials for the present wound dressing include thermoplasticelastomers and curable systems.

The backing layer is capable of forming a relatively fluid-tight seal orclosure over the wound and/or around the inlet and outlet pipe(s).

However, in particular around the periphery of the wound dressing,outside the relatively fluid-tight seal, it is preferably of a materialthat has a high moisture vapour permeability, to prevent maceration ofthe skin around the wound. It may also be a switchable material that hasa higher moisture vapour permeability when in contact with liquids, e.g.water, blood or wound exudate. This may, e.g. be a material that is usedin Smith & Nephew's Allevyn™, IV3000™ and OpSite™ dressings.

The periphery of the wound-facing face of the backing layer may bear anadhesive film, for example, to attach it to the skin around the wound.This may, e.g. be a pressure-sensitive adhesive, if that is sufficientto hold the wound dressing in place in a fluid-tight seal around theperiphery of the wound-facing face of the wound dressing.

Alternatively or additionally, where appropriate a light switchableadhesive could be used to secure the dressing in place to preventleakage. (A light switchable adhesive is one the adhesion of which isreduced by photocuring. Its use can be beneficial in reducing the traumaof removal of the dressing.)

Thus, the backing layer may have a flange or lip extending around theproximal face of the backing layer, of a transparent or translucentmaterial (for which it will be understood that materials that are listedabove are amongst those that are suitable). This bears a film of a lightswitchable adhesive to secure the dressing in place to prevent leakageon its proximal face, and a layer of opaque material on its distal face.

To remove the dressing and not cause excessive trauma in removal of thedressing, the layer of opaque material on the distal face of the flangeor lip extending around the proximal wound is removed prior toapplication of radiation of an appropriate wavelength to the flange orlip.

If the periphery of the wound dressing, outside the relativelyfluid-tight seal, that bears an adhesive film to attach it to the skinaround the wound, is of a material that has a high moisture vapourpermeability or is a switchable material, then the adhesive film, ifcontinuous, should also have a high or switchable moisture vapourpermeability, e.g. be an adhesive such as used in Smith & Nephew'sAllevyn™, IV3000™ and OpSite™ dressings.

Where a vacuum is applied to hold the wound dressing in place in afluid-tight seal around the periphery of the wound-facing face of thewound dressing, the wound dressing may be provided with a siliconeflange or lip to seal the dressing around the wound. This removes theneed for adhesives and associated trauma to the patient's skin.

Where the interior of, and the flow of irrigant and/or wound exudate toand through, the dressing is under any significant positive pressure,which will tend to act at peripheral points to lift and remove thedressing off the skin around the wound.

In such use of the apparatus, it may thus be necessary to providesecuring means for forming and maintaining such a seal or closure overthe wound against such positive pressure on the wound, to act atperipheral points for this purpose. Examples of such securing meansinclude light switchable adhesives, as above, to secure the dressing inplace to prevent leakage. Since the adhesion of a light switchableadhesive is reduced by photocuring, thereby reducing the trauma ofremoval of the dressing, a film of a more aggressive adhesive may beused, e.g. on a flange, as above.

Examples of suitable fluid adhesives for use in more extreme conditionswhere trauma to the patient's skin is tolerable include ones thatconsist essentially of cyanoacrylate and like tissue adhesives, appliedaround the edges of the wound and/or the proximal face of the backinglayer of the wound dressing, e.g. on a flange or lip.

Further suitable examples of such securing means include adhesive (e.g.with pressure-sensitive adhesive) and non-adhesive, and elastic andnon-elastic straps, bands, loops, strips, ties, bandages, e.g.compression bandages, sheets, covers, sleeves, jackets, sheathes, wraps,stockings and hose, e.g. elastic tubular hose or elastic tubularstockings that are a compressive fit over a limb wound to apply suitablepressure to it when the therapy is applied in this way; and inflatablecuffs, sleeves, jackets, trousers, sheathes, wraps, stockings and hosethat are a compressive fit over a limb wound to apply suitable pressureto it when the therapy is applied in this way.

Such securing means may each be laid out over the wound dressing toextend beyond the periphery of the backing layer of the wound dressing,and as appropriate will be adhered or otherwise secured to the skinaround the wound and/or itself and as appropriate will apply compression(e.g. with elastic bandages, stockings) to a degree that is sufficientto hold the wound dressing in place in a fluid-tight seal around theperiphery of the wound,

Such securing means may each be integral with the other components ofthe dressing, in particular the backing layer.

Alternatively, it may be permanently attached or releasably attached tothe dressing, in particular the backing layer, with an adhesive film,for example, or these components may be a Velcro™, push snap ortwist-lock fit with each other.

The securing means and the dressing may be separate structures,permanently unattached to each other.

In a more suitable layout for higher positive pressures on the wound, astiff flange or lip extends around the periphery of the proximal face ofthe backing layer of the wound dressing. The flange or lip is concave onits proximal face to define a peripheral channel or conduit. It has asuction outlet that passes through the flange or lip to communicate withthe channel or conduit and may be connected to a device for applying avacuum, such as a pump or a piped supply of vacuum.

The backing layer may be integral with or attached, for example byheat-sealing, to the flange or lip extending around its proximal face.

To form the relatively fluid-tight seal or closure over a wound that isneeded and to prevent passage of irrigant and/or exudate under theperiphery of the wound-facing face of the wound dressing, in use of theapparatus, the dressing is set on the skin around the wound. The devicethen applies a vacuum to the interior of the flange or lip, thus formingand maintaining a seal or closure acting at peripheral points around thewound against the positive pressure on the wound.

With all the foregoing means of attachment, and means for forming andmaintaining a seal or closure over the wound, against positive ornegative pressure on the wound at peripheral points around the wound,the wound dressing sealing periphery is preferably of a generally roundshape, such as an ellipse, and in particular circular.

To form the relatively fluid-tight seal or closure over a wound andaround the inlet pipe(s) and outlet pipe(s) at the point at which theypass through and/or under the wound-facing face, the backing layer maybe integral with these other components.

The components may alternatively just be a push, snap or twist-lock fitwith each other, or adhered or heat-sealed together.

The or each inlet pipe or outlet pipe may be in the form of an aperture,such as a funnel, hole, opening, orifice, luer, slot or port forconnection as a female member respectively to a mating end of a fluidtube and/or fluid supply tube (optionally or as necessary via means forforming a tube, pipe or hose, or nozzle, hole, opening, orifice, luer,slot or port for connection as a male member respectively to a matingend of a fluid tube and/or fluid supply tube (optionally or as necessaryvia means for supply flow regulation) or a fluid offtake tube.

Where the components are integral they will usually be made of the samematerial (for which it will be understood that materials that are listedabove are amongst those that are suitable).

Where, alternatively, they are a push, snap or twist-lock fit, the maybe of the same material or of different materials. In either case,materials that are listed above are amongst those that are suitable forall the components.

The or each pipe will generally pass through, rather than under thebacking layer. In such case, the backing layer may often have a rigidand/or resiliently inflexible or stiff area to resist any substantialplay between the or each pipe and the or each mating tube, ordeformation under pressure in any direction.

It may often be stiffened, reinforced or otherwise strengthened by aboss projecting distally (outwardly from the wound) around each relevanttube, pipe or hose, or nozzle, hole, opening, orifice, luer, slot orport for connection to a mating end of a fluid tube and/or fluid supplytube or fluid offtake tube.

Alternatively or additionally, where appropriate the backing layer mayhave a stiff flange or lip extending around the proximal face of thebacking layer to stiffen, reinforce or otherwise strengthen the backinglayer.

Where a simple pipe is used to supply the irrigant to the wound, thismay not provide a system to distribute irrigant over a sufficientfunctional surface area to irrigate the wound at a practical rate to besuitable for use, in particular in chronic wound aspiration andirrigation, which may contain relatively high concentrations ofmaterials that are deleterious to wound healing.

It may be advantageous to provide a system where wound irrigant may bedistributed more evenly, or pass in a more convoluted path under thedressing over the wound bed.

Accordingly, one form of the dressing is provided with a ‘tree’ form ofpipes, tubes or tubules that radiate from an inlet manifold to the woundbed to end in apertures and deliver the aspirating fluid directly to thewound bed via the apertures. Similarly, there is optionally an outletmanifold from which tubules radiate and run to the wound bed to end inopenings and collect the fluid directly from the wound bed.

The pipes, etc. may radiate regularly or irregularly through the woundin use, respectively from the inlet or outlet manifold, althoughregularly may be preferred. A more suitable layout for deeper wounds isone in which the pipes, etc. radiate hemispherically and concentrically,to the wound bed.

For shallower wounds, examples of suitable forms of such layout of thepipes, etc. include ones in which the pipes, etc. radiate in a flattenedhemiellipsoid and concentrically, to the wound bed.

Other suitable forms of layout of the pipes, etc. include one which havepipes, tubes or tubules extending from the inlet pipe(s) and/or outletpipe(s) at the point at which they pass through and/or under thewound-facing face of the backing layer to run over the wound bed. Thesemay have a blind bore with perforations, apertures, holes, openings,orifices, slits or slots along the pipes, etc.

These pipes, etc. then effectively form an inlet pipe manifold thatdelivers the aspirating fluid directly to the wound bed or outlet pipeor collects the fluid directly from the wound respectively. It does sovia the holes, openings, orifices, slits or slots in the tubes, pipes,tubules, etc. over most of the wound bed under the backing layer.

It may be desirable that the tubes, pipes or tubules are resilientlyflexible, e.g. elastomeric, and preferably soft, structures with goodconformability in the wound and the interior of the wound dressing.

When the therapy is applied in this way, the layout of the tubes, pipes,tubules, etc. may depend on the depth and/or capacity of the wound.

Thus, for shallower wounds, examples of suitable forms of such layout ofthe tubes, pipes, tubules, etc. include ones that consist essentially ofone or more of the tubes, etc in a spiral.

A more suitable layout for deeper wounds when the therapy is applied inthis way may be one which comprises one or more of the tubes, etc in ahelix or spiral helix.

Other suitable layouts for shallower wounds include one which haveblind-bore, perforated inlet pipe or outlet pipe manifolds that aspiratefluid in the wound when the dressing is in use.

One or both of these may be such a form, the other may be, e.g. one ormore straight blind-bore, perforated radial tubes, pipes or nozzles.

A preferred form of inlet pipe (or less usually) outlet pipe manifoldthat delivers the aspirating fluid directly to the wound bed or collectsthe fluid directly from the wound respectively is one that comprise oneor more conformable hollow bodies defined by a film, sheet or membrane,such as a bag, chamber, pouch or other structure, filled with theirrigant (or less usually aspirate) from the wound, passing throughperforations, apertures, holes, openings, orifices, slits or slots inthe film, sheet or membrane defining the hollow body or hollow bodies.

These may be of small cross-dimension, so that they may then effectivelyform microperforations, microapertures or pores in a permeable integer,for example the polymer film, sheet or membrane.

This type of manifold for irrigation (more usually) provides the highestuniformity in the flow distribution of irrigant over the wound at apractical rate to be suitable for use, in particular in chronic woundaspiration and irrigation, and hence to provide a system where materialsthat are beneficial in promoting wound healing, such as growth factors,cell matrix components, and other physiologically active components ofthe exudate from a wound, are distributed more evenly under the dressingover the wound bed.

This type of manifold for irrigation (more usually) is noted below withregard to wound fillers under the backing layer, since it is aresiliently flexible, e.g. elastomeric, and soft, structure with goodconformability to wound shape.

It is urged by its own resilience against the backing layer to applygentle pressure on the wound bed, and is therefore also capable ofacting as a wound filler. The film, sheet or membrane, often has a(generally uniform) thickness similar to that of films or sheets used inconventional wound dressing backing layers.

Another suitable layout is one in which an inlet pipe and/or outlet pipemanifold that delivers the aspirating fluid directly to the wound bed orcollects the fluid directly from the wound respectively via inlet and/oroutlet tubes, pipes or tubules,

and the inlet manifold and/or outlet manifold is formed by slots inlayers permanently attached to each other in a stack, and the inletand/or outlet tubes, pipes or tubules are formed by apertures throughlayers permanently attached to each other in a stack.

As also mentioned herein, the backing layer that is applied may be anythat is appropriate to the present system of therapy and permits apositive or negative pressure of up to 50% atm., more usually up to 25%atm. to be applied to the wound.

It is thus often a microbe-impermeable film, sheet or membrane, which issubstantially flat, depending on any pressure differential on it, andoften with a (generally uniform) thickness similar to such films orsheets used in conventional wound dressings, i.e. up to 100 micron,preferably up to 50 micron, more preferably up to 25 micron, and of 10micron minimum thickness.

The backing layer may often have a rigid and/or resiliently inflexibleor stiff area to resist any substantial play between other componentsthat are not mutually integral, and may be stiffened, reinforced orotherwise strengthened, e.g. by a projecting boss.

Such a form of dressing would not be very conformable to the wound bed,and may effectively form a chamber, hollow or cavity defined by abacking layer and the wound bed under the backing layer.

It may be desirable that the interior of the wound dressing conform tothe wound bed, even for a wound in a highly exuding state. Accordingly,one form of the dressing is provided with a wound filler under thebacking layer.

This is favourably a resiliently flexible, e.g. elastomeric, andpreferably soft, structure with good conformability to wound shape. Itis urged by its own resilience against the backing layer to apply gentlepressure on the wound bed. The wound filler may be integral with theother components of the dressing, in particular the backing layer.Alternatively, it may be permanently attached to them/it, with anadhesive film, for example, or by heat-sealing, e.g. to a flange or lipextending from the proximal face, so a not to disrupt the relativelyfluid-tight seal or closure over the wound that is needed.

Less usually, the wound filler is releasably attached to the backinglayer, with an adhesive film, for example, or these components may be apush, snap or twist-lock fit with each other.

The wound filler and the backing layer may be separate structures,permanently unattached to each other.

The wound filler may be or comprise a solid integer, favourably aresiliently flexible, e.g. elastomeric, and preferably soft, structurewith good conformability to wound shape. Examples of suitable forms ofsuch wound fillers are foams formed of a suitable material, e.g. aresilient thermoplastic.

Preferred materials for the fillers include reticulated filtrationpolyurethane foams with small apertures or pores.

Alternatively or additionally, it may be in the form of, or comprise oneor more conformable hollow bodies defined by a film, sheet or membrane,such as a bag, chamber, pouch or other structure, filled with a fluid orsolid that urges it to the wound shape.

The film, sheet or membrane, often has a (generally uniform) thicknesssimilar to that of films or sheets used in conventional wound dressingbacking layers.

That is, up to 100 micron, preferably up to 50 micron, more preferablyup to 25 micron, and of 10 micron minimum thickness, and is oftenresiliently flexible, e.g. elastomeric, and preferably soft.

Such a filler is often integral with the other components of thedressing, in particular the backing layer, or permanently attached tothem/it, with an adhesive film, for example, or by heat-sealing, e.g. toa flange

Examples of suitable fluids contained in the hollow body or bodiesdefined by a film, sheet or membrane include gases, such as air,nitrogen and argon, more usually air, at a small positive pressure aboveatmospheric; and liquids, such as water, saline.

Examples also include gels, such as silicone gels, e.g. CaviCare™ gel,or preferably cellulosic gels, for example hydrophilic cross-linkedcellulosic gels, such as Intrasite™ cross-linked materials.

Examples also include aerosol foams, where the gaseous phase of theaerosol system is air or an inert gas, such as nitrogen or argon, moreusually air, at a small positive pressure above atmospheric; and solidparticulates, such as plastics crumbs.

In an alternative embodiment the filler of the apparatus canconveniently be an expandable or contractible module which is the meansto apply stress to the wound bed. In one preferred embodiment the modulecomprises an inflatable body, e.g. an inflatable pouch or bag.

Of course, if the backing layer is a sufficiently conformable and/ore.g. an upwardly dished sheet, the backing layer may lie under the woundfiller, rather than vice versa.

In this type of layout, in order for the wound filler to urge the wounddressing towards the wound bed, it will usually have to be firmlyadhered or otherwise releasably attached to the skin around the wound.This is especially the case in those embodiments where the wound fillerand the backing layer are separate structures, permanently unattached toeach other.

In such a layout for deeper wounds when the therapy is applied in thisway, the means for such attachment may also form and maintain a seal orclosure over the wound.

Where the filler is over the backing layer, and the fluid inlet pipe(s)and outlet pipe(s) pass through the wound-facing face of the backinglayer, they may run through or around the wound filler over the backinglayer.

One form of the dressing is provided with a wound filler under thebacking layer that is or comprises a resiliently flexible, e.g.elastomeric, and preferably soft, hollow body defined by a film, sheetor membrane, such as a bag, chamber, pouch or other structure.

It has apertures, holes, openings, orifices, slits or slots, or tubes,pipes, tubules or nozzles. It communicates with at least one inlet oroutlet pipe through at least one aperture, hole, opening, orifice, slitor slot.

The fluid contained in the hollow body may then be the aspirating orirrigating fluid in the apparatus.

The hollow body or each of the hollow bodies then effectively forms aninlet pipe or outlet pipe manifold that delivers the aspirating fluiddirectly to the wound bed or collects the fluid directly from the woundrespectively via the holes, openings, orifices, slits or slots, or thetubes, pipes or hoses, etc. in the film, sheet or membrane.

When the therapy is applied in this way, the type of the filler may alsobe largely determined by the depth and/or capacity of the wound.

Thus, for shallower wounds, examples of suitable wound fillers as acomponent of a wound dressing include ones that consist essentially ofone or more conformable hollow bodies defining an inlet pipe and/oroutlet pipe manifold that delivers the aspirating fluid directly to thewound bed or collects the fluid directly from the wound.

A more suitable wound filler for deeper wounds when the therapy isapplied in this way may be one which comprises one or more conformablehollow bodies defined by, for example a polymer film, sheet or membrane,that at least partly surround(s) a solid integer. This may provide asystem with better rigidity for convenient handling.

The wound filler under the backing layer effectively may form an (or beformed by) inlet pipe or outlet pipe manifold.

If not, in order for aspiration and/or irrigation of the wound bed tooccur, it is appropriate for one or more bores, channels, conduits,passages, pipes, tubes, tubules and/or spaces, etc. to run from thepoint at which the fluid inlet pipe(s) and outlet pipe(s) pass throughand/or under the wound-facing face of the backing layer through oraround the wound filler under the backing layer.

Less usually, the wound filler maybe an open-cell foam with pores thatmay form such bores, channels, conduits, passages and/or spaces throughthe wound filler under the backing layer.

Where the filler is or comprises one or more conformable hollow bodiesdefined by, for example a polymer film, sheet or membrane, it may beprovided with means for admitting fluids to the wound bed under thewound dressing.

These may be in the form of pipes, tubes, tubules or nozzles runningfrom the point at which the fluid inlet pipe(s) and outlet pipe(s) passthrough and/or under the wound-facing face of the backing layer throughor around the wound filler under the backing layer.

All of the suitable layouts for shallower wounds that compriseblind-bore, perforated inlet pipe or outlet pipe manifolds that aspiratefluid in the wound when the dressing is in use, that are describedhereinbefore, may be used under a wound filler under the backing layer.

In brief, suitable layouts include ones where one or both manifolds areannular or toroidal (regular, e.g. elliptical or circular or irregular),optionally with blind-bore, perforated radial tubes, pipes or nozzles,branching from the annulus or torus; and/or

in a meandering, tortuous, winding, zigzag, serpentine or boustrophedic(i.e. in the manner of a ploughed furrow) pattern, ordefined by slots in and apertures through layers attached to each otherin a stack.

The inlet and/or outlet tubes, the fluid tube and the fluid supply tube,etc. may be of conventional type, e.g. of elliptical or circularcross-section, and may suitably have a uniform cylindrical bore,channel, conduit or passage throughout their length, and suitably thelargest cross-dimension of the bore may be up to 10 mm for large torsowounds, and up to 2 mm for limb wounds.

The tube walls should suitably thick enough to withstand any positive ornegative pressure on them. However, the prime purpose of such tubes isto convey fluid irrigant and exudate through the length of the apparatusflow path, rather than to act as pressure vessels. The tube walls maysuitably be at least 25 micron thick. The bore or any perforations,apertures, holes, openings, orifices, slits or slots along the pipes,etc. or in the hollow body or each of the hollow bodies may be of smallcross-dimension. They may then effectively form a macroscopic and/ormicroscopic filter for particulates including cell debris andmicro-organisms, whilst allowing proteins and nutrients to pass through.

Such tubes, pipes or hoses, etc. through and/or around the filler,whether the latter is a solid integer and/or one or more resilientlyflexible or conformable hollow bodies, are described in further detailhereinbefore in connection with the inlet pipe(s) and outlet pipe(s).

The whole length of the apparatus for aspirating, irrigating and/orcleansing wounds should be microbe-impermeable once the wound dressingis over the wound in use.

It is desirable that the wound dressing and the interior of theapparatus for aspirating, irrigating and/or cleansing wounds of thepresent invention is sterile.

The fluid may be sterilised in the fluid reservoir and/or the rest ofthe system in which the fluid moves by ultraviolet, gamma or electronbeam irradiation.

This way, in particular reduces or eliminates contact of internalsurfaces and the fluid with any sterilising agent.

Examples of other methods of sterilisation of the fluid also includee.g. the use of:

-   -   ultrafiltration through microapertures or micropores, e.g. of        0.22 to 0.45 micron maximum cross-dimension, to be selectively        impermeable to microbes; and    -   fluid antiseptics, such as solutions of chemicals, such as        chlorhexidine and povidone iodine; metal ion sources, such as        silver salts, e.g. silver nitrate; and hydrogen peroxide        although these involve contact of internal surfaces and the        fluid with the sterilising agent.

It may be desirable that the interior of the wound dressing, the rest ofthe system in which the fluid moves, and/or the wound bed, even for awound in a highly exuding state, are kept sterile after the fluid issterilised in the fluid reservoir, or that at least naturally occurringmicrobial growth is inhibited.

Thus, materials that are potentially or actually beneficial in thisrespect may be added to the irrigant initially, and as desired theamount in increased by continuing addition. Examples of such materialsinclude antibacterial agents (some of which are listed above), andantifungal agents. Amongst those that are suitable are, for exampletriclosan, iodine, metronidazole, cetrimide, chlorhexidine acetate,sodium undecylenate, chlorhexidine and iodine.

Buffering agents, such as potassium dihydrogen phosphate/disodiumhydrogen phosphate. may be added to adjust the pH, as may localanalgesics/anaesthetics, such as lidocaine/lignocaine hydrochloride,xylocaine (adrenaline, lidocaine) and/or anti-inflammatories, to reducewound pain or inflammation or pain associated with the dressing. Inorder to combat the deposition of materials in the flow path from theirrigant, a repellent coating may be used at any point or on any integerin the path in direct contact with the fluid, e.g. on the means forproviding aspiration and/or irrigation of the wound or any desired tubeor pipe. Examples of coating materials for surfaces over which theaspirating fluid passes include:

-   -   anticoagulants, such as heparin, and    -   high surface tension materials, such as PTFE, and polyamides,        which are useful for growth factors, enzymes and other proteins        and derivatives.

The fluid reservoir for the irrigant may be of any conventional type,e.g. a tube, bag (such as a bag typically used for blood or bloodproducts, e.g. plasma, or for infusion feeds, e.g. of nutrients),chamber, pouch or other structure, e.g. of polymer film, which cancontain the irrigant fluid. The reservoir may be made of a film, sheetor membrane, often with a (generally uniform) thickness similar to thatof films or sheets used in conventional wound dressing backing layers,i.e. up to 100 micron, preferably up to 50 micron, more preferably up to25 micron, and of 10 micron minimum thickness, and is often aresiliently flexible, e.g. elastomeric, and preferably soft, hollowbody.

In all embodiments of the apparatus the type and material of the tubesthroughout the apparatus of the invention for aspirating, irrigatingand/or cleansing wounds and the fluid reservoir will be largelydetermined by their function.

To be suitable for use, in particular on chronic timescales, thematerial should be non-toxic and biocompatible, inert to any activecomponents, as appropriate of the irrigant from the fluid reservoirand/or wound exudate in the apparatus flow path, and, in any use of atwo-phase system aspiration and irrigation unit, of the dialysate thatmoves into the aspirating fluid in the apparatus.

When in contact with irrigant fluid, it should not allow any significantamounts of extractables to diffuse freely out of it in use of theapparatus.

It should be sterilisable by ultraviolet, gamma or electron beamirradiation and/or with fluid antiseptics, such as solutions ofchemicals, fluid- and microbe-impermeable once in use, and flexible.

Examples of suitable materials for the fluid reservoir include syntheticpolymeric materials, such as polyolefins, such as polyethylene, e.g.high-density polyethylene and polypropylene.

Suitable materials for the present purpose also include copolymersthereof, for example with vinyl acetate and mixtures thereof. Suitablematerials for the present purpose further include medical gradepoly(vinyl chloride).

Notwithstanding such polymeric materials, the fluid reservoir will oftenhave a stiff area to resist any substantial play between it andcomponents that are not mutually integral, such as the fluid supply tubetowards the wound dressing, and may be stiffened, reinforced orotherwise strengthened, e.g. by a projecting boss.

Materials deleterious to wound healing that are removed using theapparatus include:

oxidants, such as free radicals, e.g. peroxide and superoxide;iron II and iron III;all involved in oxidative stress on the wound bed;proteases, such as serine proteases, e.g. elastase and thrombin;cysteine proteases; matrix metalloproteases, e.g. collagenase; andcarboxyl (acid) proteases;endotoxins, such as lipopolysaccharides;autoinducer signalling molecules, such as homoserine lactonederivatives, e.g. oxo-alkyl derivatives;inhibitors of angiogenesis such as thrombospondin-1 (TSP-1), plasminogenactivator inhibitor, or angiostatin (plasminogen fragment);pro-inflammatory cytokines such as tumour necrosis factor alpha (TNFα)and interleukin 1 beta (IL-1β),oxidants, such as free radicals, e.g., e.g. peroxide and superoxide; andmetal ions, e.g. iron II and iron III, all involved in oxidative stresson the wound bed.

It is believed that aspirating wound fluid aids in removal from of thematerials deleterious to wound healing from wound exudate and/orirrigant, whilst distributing materials that are beneficial in promotingwound healing in contact with the wound.

A steady state concentration equilibrium of materials beneficial inpromoting wound healing may be set up between in the irrigant and/orwound exudate. Aspirating wound fluid aids in the quicker attainment ofthis equilibrium. Materials beneficial to wound healing that aredistributed include cytokines, enzymes, growth factors, cell matrixcomponents, biological signalling molecules and other physiologicallyactive components of the exudate and/or materials in the irrigant thatare potentially or actually beneficial in respect of wound healing, suchas nutrients for wound cells to aid proliferation, gases, such asoxygen.

The conduits through which respectively the irrigant and/or woundexudate passes to and from the wound dressing and

-   i) may have means for modular disconnection and withdrawal of the    dressing,-   ii) providing an immediate fluid-tight seal or closure over the ends    of the conduits and the cooperating tubes in the rest of the    apparatus of the invention so exposed,    to prevent continuing passage of irrigant and/or exudate.

The outlet from the means for aspirate flow regulation and/or tubes maybe collected and monitored and used to diagnose the status of the woundand/or its exudate.

Any aspirate collection vessel may be of any conventional type, e.g. atube, bag (such as a bag typically used as an ostomy bag), chamber,pouch or other structure, e.g. of polymer film, which can contain theirrigant fluid that has been bled off. In all embodiments of theapparatus, the type and material of the aspirate collection vessel willbe largely determined by its function.

To be suitable for use, the material need only be fluid-impermeable oncein use, and flexible.

Examples of suitable materials for the fluid reservoir include syntheticpolymeric materials, such as polyolefins, such as poly (vinylidenechloride).

Suitable materials for the present purpose also include polyethylene,e.g. high-density polyethylene, polypropylene, copolymers thereof, forexample with vinyl acetate and mixtures thereof.

In a further aspect of the present invention there is provided aconformable wound dressing, characterised in that it comprises a backinglayer with a wound-facing face which is capable of forming a relativelyfluid-tight seal or closure over a wound and has

at least one pipe, which passes through and/or under the wound-facingface to allow irrigation and/or aspiration of the wound, wherein thepoint at which the or each inlet pipe and the or each outlet pipe passesthrough and/or under the wound-facing face forming a relativelyfluid-tight seal or closure over the wound; and means for stressing thewound bed and optionally tissue surrounding the wound.

The dressing is advantageously provided for use in a bacteria-proofpouch.

Examples of suitable forms of such wound dressings are as described byway of example hereinbefore.

In a third aspect of the present invention there is provided a method oftreating wounds to promote wound healing using the apparatus foraspirating, irrigating and/or cleansing wounds of the present invention.

The present invention will now be described by way of example only withreference to the accompanying drawings in which, in all schematics, themeans for applying stress to the wound bed omitted for clarity.

FIG. 1 is a schematic view of an apparatus for aspirating, irrigatingand/or cleansing a wound according to the present invention that has asingle device for moving fluid through the wound applied to the aspiratein the fluid offtake tube downstream of and away from the wounddressing,

in combination with means for supply flow regulation, connected to afluid supply tube, and means for aspirate flow regulation, connected toa fluid offtake tube.

FIG. 2 is a schematic view of another apparatus for aspirating,irrigating and/or cleansing a wound according to the present inventionthat has

a first device for moving fluid through the wound applied to theaspirate in the fluid offtake tube downstream of and away from the wounddressing, with means for aspirate flow regulation, connected to a fluidofftake tube; and a second device for moving fluid through the woundapplied to the irrigant in the fluid supply tube upstream of and towardsthe wound dressing.

FIGS. 3 to 8 are views of conformable wound dressings for aspiratingand/or irrigating wounds.

In these, FIGS. 3 a to 5 a are plan views of the wound dressings, andFIGS. 3 b, 4 b, 5 b, 6, 7 and 8 a are cross-sectional side views of thewound dressings. FIG. 8 b shows an isometric view of a stack of layersin an exploded inlet manifold.

FIGS. 9 a to d are variants of a two-pump system with essentiallyidentical, and identically numbered, components as in FIG. 2, exceptthat there is a pump bypass loop, a filter downstream of the aspiratecollection vessel, and a bleed regulator, such as a rotary valve,connected to the fluid offtake tube or to the wound space, for theregulation of the positive or negative pressure applied to the wound.

FIGS. 10 a to c are variants of a two-pump system with essentiallyidentical, and identically numbered, components as in FIG. 9, exceptthat they have various means for varying the regulation of the positiveor negative pressure applied to the wound.

FIGS. 11 a and b are variants of a two-pump system with essentiallyidentical, and identically numbered, components as in FIGS. 9 a to d.However, they have alternative means for handling the aspirate flow tothe aspirate collection vessel under negative or positive pressure tothe wound in simultaneous aspiration and irrigation of the wound,including in FIG. 11 b a third device for moving fluid into a waste bag.

FIG. 12 is a single-pump system essentially with the omission from theapparatus of FIGS. 9 a to d of the second device for moving irrigantfluid into the wound dressing.

Referring to FIG. 1, the apparatus (1) for aspirating, irrigating and/orcleansing wounds comprises a conformable wound dressing (2), having

a backing layer (3) which is capable of forming a relatively fluid-tightseal or closure (4) over a wound (5) andone inlet pipe (6) for connection to a fluid supply tube (7), whichpasses through the wound-facing face of the backing layer (5) at (8),andone outlet pipe (9) for connection to a fluid offtake tube (10), whichpasses through the wound-facing face at (11),the points (8), (11) at which the inlet pipe and the outlet pipe passesthrough and/or under the wound-facing face forming a relativelyfluid-tight seal or closure over the wound;the inlet pipe being connected via means for supply flow regulation,here a valve (14), by the fluid supply tube (7) to a fluid reservoir(12), andthe outlet pipe (9) being connected via means for aspirate flowregulation, here a valve (16) and a fluid offtake tube (10) to waste,e.g. to a collection bag (not shown);a device for moving fluid through the wound (17), here a diaphragm pump(18), e.g. preferably a small portable diaphragm pump, acting on thefluid aspiration tube (13) to apply a low negative pressure on thewound; andthe valve (14) in the fluid supply tube (7), the valve (16) in the fluidofftake tube (10), and the diaphragm pump (18), providing means forproviding simultaneous aspiration and irrigation of the wound (17),such that fluid may be supplied to fill the flowpath from the fluidreservoir via the fluid supply tube (via the means for supply flowregulation) and moved by the device through the flow path.

The Operation of the Apparatus is as Described Hereinbefore.

Referring to FIG. 2, the apparatus (21) is a variant two-pump systemwith essentially identical, and identically numbered, components as inFIG. 1, except that

there is no means for supply flow regulation in the fluid supply tube(7) from the fluid reservoir (12B), andthere isa first device for moving fluid through the wound (17), here a diaphragmpump (18A), e.g. preferably a small portable diaphragm pump, acting onthe fluid aspiration tube (13) downstream of and away from the wounddressing to apply a low negative pressure on the wound; withmeans for aspirate flow regulation here a valve (16) connected to thefluid offtake tube (10) and a vacuum vessel (aspirate collection jar)(12A); anda second device for moving fluid through the wound (17), here aperistaltic pump (18B), e.g. preferably a small portable diaphragm pump,applied to the irrigant in the fluid supply tube (7) upstream of andtowards the wound dressing,the first device (18A) and second device (18B), and the valve (16) inthe fluid offtake tube (10), and the diaphragm pump (18), providingmeans for providing simultaneous aspiration and irrigation of the wound(17), such that fluid may be supplied to fill the flowpath from thefluid reservoir via the fluid supply tube (via the means for supply flowregulation) and moved by the devices through the flow path.

The Operation of the Apparatus is as Described Hereinbefore

Referring to FIGS. 3 a and 3 b, a wound dressing suitable for shallowerwounds is shown. This comprises a circular backing layer (42) and acircular upwardly dished first membrane (61) with apertures (62) that ispermanently attached to the backing layer (42) by heat-sealing to form acircular pouch (63).

The pouch (63) communicates with the inlet pipe (46) through a hole(64), and thus effectively forms an inlet pipe manifold that deliversthe circulating fluid directly to the wound when the dressing is in use.

An annular second membrane (65) with openings (66) is permanentlyattached to the backing layer (42) by heat-sealing to form an annularchamber (67) with the layer (42).

The chamber (67) communicates with the outlet pipe (47) through anorifice (68), and thus effectively forms an outlet pipe manifold thatcollects the fluid directly from the wound when the dressing is in use.

Referring to FIGS. 4 a and 4 b, a variant of the dressing of FIGS. 3 aand 3 b that is a more suitable form for deeper wounds is shown.

This comprises a circular backing layer (42) and a filler (69), in theform of an inverted frustroconical, solid integer, here a resilientelastomeric foam, formed of a thermoplastic, or preferably across-linked plastics foam.

It is permanently attached to the backing layer (42), with an adhesivefilm (not shown) or by heat-sealing.

A circular upwardly dished sheet (70) lies under and conforms to, but isa separate structure, permanently unattached to, the backing layer (42)and the solid integer (69).

A circular upwardly dished first membrane (71) with apertures (72) ispermanently attached to the sheet (70) by heat-sealing to form acircular pouch (73) with the sheet (70).

The pouch (73) communicates with the inlet pipe (46) through a hole(74), and thus effectively forms an inlet pipe manifold that deliversthe circulating fluid directly to the wound when the dressing is in use.

An annular second membrane (75) with openings (76) is permanentlyattached to the sheet (70) by heat-sealing to form an annular chamber(77) with the sheet (70).

The chamber (77) communicates with the outlet pipe (77) through anorifice (78), and thus effectively forms an outlet pipe manifold thatcollects the fluid directly from the wound when the dressing is in use.

Alternatively, where appropriate the dressing may be provided in a formin which the circular upwardly dished sheet (70) functions as thebacking layer and the solid filler (69) sits on the sheet (70) as thebacking layer, rather than under it. The filler (69) is held in placewith an adhesive film or tape, instead of the backing layer (42). Thisis illustrated in FIGS. 4 a and 4 b.

Referring to FIGS. 5 a and 5 b, a dressing that is a more suitable formfor deeper wounds is shown.

This comprises a circular backing layer (42) and a filler (79), in theform of an inverted generally hemispherical integer, e.g. a resilientelastomeric foam or a hollow body filled with a fluid, e.g. a gel thaturges it to the wound shape, and permanently unattached to the backinglayer.

The inlet pipe (46) and outlet pipe (47) are mounted peripherally in thebacking layer (42).

A circular upwardly dished sheet (80) lies under and conforms to, but isa separate structure, permanently unattached to, the backing layer (42)and the filler (79).

A circular upwardly dished bilaminate membrane (81) has a closed channel(82) between its laminar components, with

perforations (83) along its length on the outer surface (84) of the dishformed by the membrane (81) andan opening (85) at the outer end of its spiral helix, through which thechannel (82) communicates with the inlet pipe (46),and thus effectively forms an inlet pipe manifold that delivers thecirculating fluid directly to the wound when the dressing is in use.

The membrane (81) also has apertures (86) between and along the lengthof the turns of the channel (82).

The inner surface (87) of the dish formed by the membrane (81) ispermanently attached at its innermost points (88) with an adhesive film(not shown) or by heat-sealing to the sheet (80). This defines a matingclosed spirohelical conduit (89).

At the outermost end of its spiral helix, the conduit (89) communicatesthrough an opening (90) with the outlet pipe (47) and is thuseffectively an outlet manifold to collect the fluid directly from thewound via the apertures (86).

Referring to FIGS. 6 and 7, these forms of the dressing are providedwith a wound filler (348) under a circular backing layer (42).

This comprises respectively a generally downwardly domed or oblatelyspheroidal conformable hollow body, defined by a membrane (349) which isfilled with a fluid, here air or nitrogen, that urges it to the woundshape.

An inflation inlet pipe (350), inlet pipe (46) and outlet pipe (47) aremounted centrally in the boss (351) in the backing layer (42) above thehollow body (348). The inflation inlet pipe (350) communicates with theinterior of the hollow body (348), to permit inflation of the body(348). Though such inflation of the hollow body (348) the stress appliedto the wound can be varied by varying the pressure within the hollowbody (348).

The inlet pipe (46) extends in a pipe (352) effectively through thehollow body (348). The outlet pipe (47) extends radially immediatelyunder the backing layer (42).

In FIG. 6, the pipe (352) communicates with an inlet manifold (353),formed by a membrane (361) with apertures (362) that is permanentlyattached to the filler (348) by heat-sealing. It is filled with foam(363) formed of a suitable material, e.g. a resilient thermoplastic.Preferred materials include reticulated filtration polyurethane foamswith small apertures or pores.

The filler (348) is permanently attached to the backing layer via a boss(351), which is e.g. heat-sealed to the backing layer (42).

In FIG. 7, the outlet pipe (47) communicates with a layer of foam (364)formed of a suitable material, e.g. a resilient thermoplastic. Again,preferred materials include reticulated filtration polyurethane foamswith small apertures or pores.

In both of FIGS. 6 and 7, in use, the pipe (352) ends in one or moreopenings that deliver the irrigant fluid directly from the wound bedover an extended area.

Similarly, the outlet pipe (47) effectively collects the fluid radiallyfrom the wound periphery when the dressing is in use.

The form of the dressing shown in FIGS. 6 and 7 is a more suitablelayout for deeper wounds.

Referring to FIG. 8 (a and b), another form for deeper wounds is shown.This comprises a circular, or more usually square or rectangular backinglayer (342) and a chamber (363) in the form of a deeply indented discmuch like a multiple Maltese cross or a stylised rose.

This is defined by an upper impervious membrane (361) and a lower porousfilm (362) with apertures (364) that deliver the irrigant fluid directlyto the wound bed over an extended area, and thus effectively forms aninlet manifold. Three configurations of the chamber (363) are shown inFIG. 8 b, all of which are able to conform well to the wound bed by thearms closing in and possibly overlapping in insertion into the wound.

The space above the chamber (363) is filled with a wound filler (348)under the backing layer (342). This comprises an oblately spheroidalconformable hollow body, defined by a membrane (349) that can be filledwith a fluid, here air or nitrogen, that urges it to the wound shape. Aninflation inlet pipe (350) is mounted centrally in a first boss (370) inthe backing layer (342) above the hollow body (348). The inflation inletpipe (350) communicates with the interior of the hollow body (348), topermit inflation of the body (348). Again, this inflation of the hollowbody (348) is conveniently a means to apply stress to the wound.

A moulded hat-shaped boss (351) is mounted centrally on the upperimpervious membrane (361) of the chamber (363). It has three internalchannels, conduits or passages through it (not shown), each with entryand exit apertures.

The filler (348) is attached to the membrane (361) of the chamber (363)by adhesive, heat welding or a mechanical fixator, such as a cooperatingpin and socket.

An inflation inlet pipe (350), inlet pipe (346) and outlet pipe (347)pass under the edge of the proximal face of the backing layer (342) ofthe dressing.

They extend radially immediately under the filler (348) and over themembrane (361) of the chamber (363) to each mate with an entry aperturein the boss (351).

An exit to the internal channel, conduit or passage through it thatreceives the inflation inlet pipe (350) communicates with the interiorof the hollow filler (348), to permit inflation.

An exit to the internal channel, conduit or passage that receives theinlet pipe (346) communicates with the interior of the chamber (363) todeliver the irrigant fluid via the chamber (363) to the wound bed overan extended area.

Similarly, an exit to the internal channel, conduit or passage thatreceives the outlet pipe (347) communicates with the space above thechamber (363) and under the wound filler (348), and collects flow ofirrigant and/or wound exudate radially from the wound periphery.

Referring to FIG. 9 a, the apparatus (21) is a variant two-pump systemwith essentially identical, and identically numbered, components as inFIG. 2.

Thus, there is a means for supply flow regulation, here a valve (14) inthe fluid supply tube (7) from the fluid reservoir (12B), and

a first device for moving fluid through the wound (17), here afixed-speed diaphragm pump (18A), e.g. preferably a small portablediaphragm pump, acting not on the fluid aspiration tube (13), but on anair aspiration tube (113) downstream of and away from an aspiratecollection vessel (12A) to apply a low negative pressure on the woundthrough the aspirate collection vessel (12A); witha second device for moving fluid through the wound (17), here afixed-speed peristaltic pump (18B), e.g. preferably a small portableperistaltic pump, applied to the irrigant in the fluid supply tube (7)upstream of and towards the wound dressing,the first device (18A) and second device (18B), and the valve (14) inthe fluid supply tube (7), providing means for providing simultaneousaspiration and irrigation of the wound (17), such that fluid may besupplied to fill the flowpath from the fluid reservoir via the fluidsupply tube (via the means for supply flow regulation) and moved by thedevices through the flow path.

There is no means for aspirate flow regulation, e.g. a valve connectedto the fluid offtake tube (10).

Since first device (18A) and second device (18B) are fixed-speed, thevalve (14) in the fluid supply tube (7) provides the sole means forvarying the irrigant flow rate and the low negative pressure on thewound.

The Following Extra Features are Present:

The second device, the fixed-speed peristaltic pump (18B), is providedwith means for avoiding over-pressure, in the form of a bypass loop witha non-return valve (115). The loop runs from the fluid supply tube (7)downstream of the pump (18B) to a point in the fluid supply tube (7)upstream of the pump (18B).

A pressure monitor (116) connected to the fluid offtake tube (10) has afeedback connection to a bleed regulator, here a motorised rotary valve(117) on a bleed tube (118) running to and centrally penetrating the topof the aspirate collection vessel (12A). This provides means for holdingthe low negative pressure on the wound at a steady level.

A filter (119) downstream of the aspirate collection vessel (12A)prevents passage of gas- (often air-) borne particulates, includingliquids and micro-organisms, from the irrigant and/or exudate thatpasses into the aspirate collection vessel (12A) into the first device(18A), whilst allowing the carrier gas to pass through the airaspiration tube (113) downstream of it to the first device (18A). Theoperation of the apparatus is as described hereinbefore

Referring to FIG. 9 b, this shows an alternative layout of theessentially identical, and identically numbered, components in FIG. 9 adownstream of point A in FIG. 9 a. The bleed tube (118) runs to the airaspiration tube (113) downstream of the filter (119), rather than intothe aspirate collection vessel (12 a). This provides means for holdingthe low negative pressure on the wound at a steady level. The operationof the apparatus is as described hereinbefore

Referring to FIG. 9 c, this shows an alternative layout of theessentially identical, and identically numbered, components in FIG. 9 aupstream of point B in FIG. 9 a. The second device (18B) is avariable-speed pump, and the valve (14) in the fluid supply tube (7) isomitted. The second device (18B) is the sole means for varying theirrigant flow rate and the low negative pressure on the wound. Theoperation of the apparatus is as described hereinbefore

Referring to FIG. 9 d, this shows an alternative layout of theessentially identical, and identically numbered, components in FIG. 9 adownstream of point B in FIG. 9 a.

The pressure monitor (116) is connected to a monitor offtake tube (120)and has a feedback connection to the bleed regulator, motorised rotaryvalve (117) on a bleed tube (118) running to the monitor offtake tube(120). This provides means for holding the low negative pressure on thewound at a steady level. The operation of the apparatus is as describedhereinbefore

Referring to FIG. 10 a, this shows another alternative layout of theessentially identical, and identically numbered, components in FIG. 9 adownstream of point B in FIG. 9 a. The pressure monitor (116) isconnected to a monitor offtake tube (120) and has a feedback connectionto a means for aspirate flow regulation, here a motorised valve (16) inthe air aspiration tube (113) downstream of the filter (119).

This provides means for aspirate flow regulation and for holding the lownegative pressure on the wound at a steady level. The operation of theapparatus is as described hereinbefore

Referring to FIG. 10 b, this shows another alternative layout of theessentially identical, and identically numbered, components in FIG. 10 adownstream of point B in FIG. 9 a. The pressure monitor (116) isconnected to a monitor offtake tube (120) and has a feedback connectionto a means for aspirate flow regulation, here a motorised valve (16), inthe fluid offtake tube (10) upstream of the aspirate collection vessel(12 a).

This provides means for aspirate flow regulation and for holding the lownegative pressure on the wound at a steady level. The operation of theapparatus is as described hereinbefore

Referring to FIG. 10 c, this shows another alternative layout of theessentially identical, and identically numbered, components in FIG. 10 adownstream of point B in FIG. 9 a. The pressure monitor (116) isconnected to a monitor offtake tube (120) and has a feedback connectionto a variable-speed first device (18A), here a variable-speed pump,downstream of the filter (119), and the valve (16) in the fluid offtaketube (10) is omitted.

This provides means for aspirate flow regulation and for holding the lownegative pressure on the wound at a steady level. The operation of theapparatus is as described hereinbefore.

Referring to FIG. 11 a, this shows another alternative layout of theessentially identical, and identically numbered, components in FIG. 10 cdownstream of point B in FIG. 9 a, and alternative means for handlingthe aspirate flow to the aspirate collection vessel under negative orpositive pressure to the wound.

The pressure monitor (116) is connected to a monitor offtake tube (120)and has a feedback connection to a variable-speed first device (18A),here a variable-speed pump, upstream of the aspirate collection vessel(12A), and the filter (119) and the air aspiration tube (113) areomitted. This provides means for aspirate flow regulation and forholding the low negative pressure on the wound at a steady level. Theoperation of the apparatus is as described hereinbefore.

Referring to FIG. 11 b, this shows another alternative layout of theessentially identical, and identically numbered, components in FIG. 10 cdownstream of point B in FIG. 9 a, and alternative means for handlingthe aspirate flow to the aspirate collection vessel under negative orpositive pressure to the wound. The pressure monitor (116) is omitted,as is the feedback connection to a variable-speed first device (18A),here a variable-speed pump, downstream of the aspirate collection vessel(12A) and the filter (119). A third device (18C), here a fixed-speedpump, provides means for moving fluid from the aspirate collectionvessel (12A) into a waste bag (12C). The operation of the apparatus isas described hereinbefore.

Referring to FIG. 12, this shows an alternative layout of theessentially identical, and identically numbered, components in FIG. 9 aupstream of point A in FIG. 9 a.

It is a single-pump system essentially with the omission from theapparatus of FIG. 9 a of the second device for moving irrigant fluidinto the wound dressing. The operation of the apparatus is as describedhereinbefore.

Demonstration of In Vitro Effects of Applying Stress to Cells in aSimulated Wound. Objective

To determine the total amount of collagen deposited by human dermalfibroblasts on silica Flexercell plates following macrostress treatmentover a period of time.

Methods Cells

Human dermal fibroblasts (HS8/BS04) were used. Experiments wereperformed whereby fibroblasts (5×10⁵ per well) were seeded in siliconemembrane 6 well plates (Flexercell), supplied by Flexcell Intl.Hillsborough, N.C. and subjected to a range of ‘macrostress’(macrostress as used in this example refers to stress applied to thecells by way of mechanical stretching) treatments for 48 hours, wherebythe cells were subjected to a strewn of 15% (i.e. 15% elongation of thecell substrate) at a frequency of 0.1 Hz on a cycle having a sine waveprofile. The Flexercell, Tension Plus™ system is a computer-driveninstrument that simulates biological strain conditions using vacuumpressure to deform cells cultured on flexible, matrix-bonded growthsurfaces of BioFlex® series culture plates. Following experimentation,media was removed, the cells were washed in PBS and stored at −70° C.until analysed for collagen levels.

The cells were exposed to sequential (SEQ) or simultaneous (SIA)irrigation/aspiration. For SIA, a flow rate of 0.1 ml per minute wasused. For sequential, 10 empty/fill cycles were performed over the 48hour period, each empty/fill taking 1 hour to complete. The media usedwas DMEM/10% FCS.

Collagen Quantification

The collagen content present on the 6 well plates was determined using ahydroxyl proline quantification assay which 2 ml papain buffer was usedto digest any collagen due to the larger surface area.

RT-PCR

Relative quantification of plasminogen inhibitor activiator 2 (PIA-2)and collagen 1a gene expression was determined using the Taqman RT-PCRmachine.

RNA Extraction

Cells were scraped from the well in RLN buffer and the RNA from 3 samplewells were pooled using one RNeasy mini column. Control RNA wasextracted from fibroblasts grown to confluence in a T175 flask.

RNA extraction from fibroblasts was performed using reagents andprotocols described in RNeasy Mini Handbook (Qiagen) and RLN buffer (50mM Tris-HCl, Sigma, lot 033K8418; 140 mM NaCl, Sigma, lot 013K8930; 1.5mM MgCl₂, Sigma, lot 082K8938; 0.5% (v/v) Igepal (Sigma, lot 102K0025);10 μl/ml β-mercaptoethanol, Sigma, lot 102K0025, made up to volume inMolecular Biology grade water (Sigma, lot, 23K2444).

Following elution from the spin column in 50 μl water, the RNA wasquantified using a spectrophotometer.

cDNA Preparation

cDNA was prepared from RNA using Omniscript reverse transcription kit(Qiagen) with Random Hexamer primers (Applied Biosystems, lot G07487).The reaction was completed by heating for 1 hour at 37° C. and stored at−20° C. until required.

RT-PCR Primers

Three gene products were selected as they had previously been shown tobe up-regulated during Flexercell Macrostress treatment (Kessler, et al,JBC, 276, 39, 36575-36585, 2001). Primers were synthesised by MWGBiotech.

Collagen 1a: F-5′ ACA TGC CGA GAC TTG AGA CTC A R-5′ GCA TCC ATA GTA CATCCT TGG TTA GG(from Wong et al, Tissue Engineering, 8, 6, 979-2002)

PAI-2: F-5′ AAT GCA TCC ACA GGG GAT TA R-5′ CGC AGA CTT CTC ACC AAA CA(Designed using Primer 3 software, sequence from accession no. H81869)

18S rRNA F-5′ CGG CTA CCA CAT CCA AGG AA R-5′ GCT GGA ATT ACC GCG GCT(18S rRNA housekeeping gene primers previously designed and synthesisedby Sigma).

SYBR Green

SYBR green reagent (Applied Biosystems, lot 0505023) master mix wasprepared as per manufacturers protocol. Briefly, 50% v/v SYBR green,0.05% primer 1, 0.05% primer 2, made up to 100% in RNase free water. 5μl cDNA template and 45111 SYBR green added per well.

PCR

The RT-PCR was performed using 7700 Taqman RT-PCR system (SOP/BC/227).The run conditions were:

-   1) 50° C. for 2 minutes-   2) 95° C. for 10 minutes-   3) 95° C. for 15 seconds-   4) 60° C. for 1 minute

Conditions 3 and 4 repeated for a total of 40 cycles.

To ensure a single PCR product had been amplified, a melt analysis onthe product was performed using the following conditions:

-   -   1) 95° C. for 15 seconds    -   2) 60° C. for 20 seconds    -   3) 95° C. for 15 seconds

A ramp time of 19.59 minutes between stage 2 and 3 was used to determinethe degradation temperature.

Results and Discussion Collagen Quantification

The amount of collagen present in each well of a six well Flexercellplate was determined using the hydroxyproline quantification assay.Fibroblast cells, seeded at either 5×10³ or 5×10⁵ per well were grown onlaminin coated plates for 72 hours. The absorbance values determinedfollowing analysis were very low, showing that the amount of collagenpresent was also very low. Unfortunately, an error was made whenpreparing the hydroxyproline standard curve whereby the stock solutionwas not diluted 10 fold so it was not possible to give an amount ofhydroxyproline present. This error would only have affected thestandards. The low values showed that this assay was not suitable formeasuring such low collagen contents.

A second hydroxyproline determination assay was performed using gaschromatography (GS-MS). This analysis also revealed very low collagencontent present in the 6 well plates.

RT-PCR

As the cells only had 72 hours to proliferate and synthesis newcollagen, a short length of time, it was decided to look for changes inthe level of gene expression, which, generally relates to changes in theamount of protein synthesised as the cells proliferate.

The genes of interest chosen to investigate were collagen 1a andplasminogen activator inhibitor 2 (PIA-2) genes as these had previouslybeen shown to be induced in stressed collagen lattices (Kessler et al,JBC, 276, 39, pp. 36575-36585, 2001). The level of gene expression ofthe genes of interest is expressed as a ratio against 18S rRNA, ahouse-keeping gene, shown previously (Kessler et al, 2001) to remain ata steady level of expression.

For the RT-PCR experiments, fibroblasts were grown and subjected to 15%strain, 0.1 Hz frequency for 48 hours, with control samples not beingsubjected to these conditions. Also, they were subjected to eithercontinuous irrigate aspiration of media (SIA), or a series of 1 hourempty/fill cycles (SEQ). All systems were kept under vacuum of ˜25 mbarbelow atmospheric.

The level of PAI-2 gene expression was determined in fibroblastssubjected to the four sets of conditions described above. The resultsare shown in table 1.

TABLE 1 SIA only 1.6 SEQ only 5.3 SIA plus macrostress 5.4 SEQ plusmacrostress 5.3

The results show that there is an increase in the level of PAI-2 geneexpression when fibroblasts in the SIA system are subjected tomacrostress (at 15% strain, 0.1 Hz frequency; n=1). However, the levelof expression is also elevated in both SEQ and SEQ plus macrostressfibroblasts. Unfortunately, due to technical difficulties during theinitial macrostress Flexercell experiments, only one set of experimentalplates were available for analysis.

CONCLUSIONS

RT-PCR analysis of PAI-2 gene expression showed an increase in the levelof expression in SIA plus macrostress compared to SIA only. Thisdemonstrates the effect of macrostress on the activity of the cells inthe in vitro wound simulation, and supports the role of macrostress inwound healing.

There was no difference in the level of expression in SEQ and SEQ plusmacrostress fibroblasts.

Due to technical difficulties, these results are from an n=1, thereforecare needs to be taken when interpreting the results. However, theresults indicate that application of macrostress to cells during SIAirrigation leads to increase levels of cell activity, and possibly ofcollagen production. This reflects on increase in healing activity wherestress is applied.

The results of the SEQ analysis are puzzling, and may be the results ofan unidentified error in the protocol. Future experiments will berequired to confirm this. An alternative hypothesis is that additionalstresses induced by the fill/empty cycle may have inadvertently resultedin stress being applied to the control population.

1) An apparatus for aspirating, irrigating and/or cleansing a wound,comprising: a) a fluid flow path, comprising a conformable wounddressing, having a backing layer which is capable of forming arelatively fluid-tight seal or closure over a wound, at least one pipewhich passes through and/or under the wound-facing face to allowirrigation and/or aspiration of the wound, wherein the point at whichthe pipe passes through and/or under the wound-facing face forming arelatively fluid-tight seal or closure over the wound, when in use; b) afluid reservoir connectable by a fluid supply tube to the pipe; and c)at least one device for moving fluid through the wound dressing to thewound and/or moving fluid from the wound; characterised in that theapparatus comprises d) means for applying stress to the wound bed andoptionally tissue surrounding the wound. 2) The apparatus of claim 1which comprises at least one inlet pipe for connection to a fluid supplytube to allow irrigation and at least one outlet pipe for connection toa fluid offtake tube to allow aspiration, each of which passes throughand/or under the wound-facing face. 3) The apparatus of claim 2 whichcomprises means for simultaneous aspiration and irrigation of the wound,such that fluid may be supplied to fill the flowpath from the fluidreservoir via the fluid supply tube while fluid is aspirated by a devicethrough the fluid offtake. 4) The apparatus of claim 1 in which themeans for applying stress to the wound bed is capable of applying anoptionally varying positive and/or negative pressure to the wound bed.5) The apparatus of claim 4 in which the means for applying stress tothe wound bed comprises at least one expandable and contractible modulecapable of applying pressure to the wound bed. 6) The apparatus of claim5 wherein the expandable and contractible module comprises afluid-inflatable body. 7) The apparatus of claim 6 wherein thefluid-inflatable body is inflatable by a gas, liquid, gas in liquidaerosol and/or a gel. 8) The apparatus of claim 7 wherein thefluid-inflatable body is a fluid-inflatable irrigant inlet manifold. 9)The apparatus of claim 8 wherein the manifold covers and contacts asignificant area of the wound bed with openings that deliver the fluiddirectly to the wound bed over an extended area. 10) The apparatus ofclaim 8 wherein the manifold comprises of one or more inflatable hollowbodies defined by a film sheet or membrane. 11) The apparatus of claim 8wherein the manifold covers 50% or greater of the wound bed. 12) Theapparatus of claim 6 wherein the fluid-inflatable body comprises afluid-inflatable wound filler. 13) The apparatus of claim 12 wherein thefluid-inflatable wound filler is an inlet manifold. 14) The apparatusclaim 6 wherein the fluid-inflatable body is partially filled with anelastically resilient material, such as an elastomeric foam. 15) Theapparatus claim 6 wherein the fluid-inflatable body comprises asubstantially flat film, sheet or membrane, defining a chamber, pouch orother structure of the backing layer. 16) The apparatus claim 6comprising an inflation and/or deflation pump for inflating or deflatingthe fluid-inflatable body. 17) The apparatus of claim 16 wherein theinflation and/or deflation pump is reversible. 18) The apparatus ofclaim 16 wherein the inflation and/or deflation pump is a piston pump orrotary pump. 19) The apparatus of claim 18 wherein the inflation and/ordeflation pump is a peristaltic pump. 20) The apparatus of claim 1 inwhich the means for applying stress to the wound bed is capable ofvarying the pressure by up 50% above and below atmospheric pressure. 21)The apparatus of claim 1 in which the means for applying stress to thewound bed is capable of varying pressure in regular or irregular cycles.22) The apparatus of claim 21 in which the frequency of regular orirregular cycles is between 1 to 48 per 24 hr. 23) The apparatus ofclaim 1 in which the means for applying stress to the wound bed iscapable of varying pressure in regular or irregular pulses. 24) Theapparatus of claim 23 in which frequencies of regular pulses for thestimulation of the healing of wounds is from 1 to 3000 per min (0.016-50Hz). 25) The apparatus of claim 24 in which maximum amplitude for thepulses is up to 10 mm Hg above and below the baseline pressure. 26) Theapparatus of claim 1 in which the means for applying stress to the woundis capable of varying pressure in regular or irregular cycles andregular or irregular pulses, the pulses being superimposed on thecycles. 27) The apparatus of claim 1 wherein the means for applyingstress to the wound bed includes a magnetic fluid in a chamber or otherhollow structure. 28) The apparatus of claim 1 wherein the means forapplying stress to the wound bed comprises means to bleed fluid into theflow path of the apparatus. 29) The apparatus of claim 3 wherein themeans for simultaneous aspiration and irrigation of the wound comprisesa first device for moving fluid through the wound applied to fluiddownstream of and away from the wound dressing, in combination with atleast one of a second device for moving fluid through the wound appliedto the irrigant in the fluid supply tube upstream of and towards thewound dressing; means for aspirate flow regulation, connected to thefluid offtake tube; and means for supply flow regulation, connected tothe fluid supply tube. 30) The apparatus of claim 29 wherein the firstand/or second device for moving fluid through the wound is avariable-throughput device. 31) The apparatus of claim 30 wherein thefirst and/or second device is a variable-speed pump. 32) The apparatusof claim 31 wherein the first and/or second device for moving fluidthrough is a reciprocating pump or a rotary pump. 33) The apparatus ofclaim 32 wherein the first device is a diaphragm pump. 34) The apparatusof claim 32 wherein the second device is a peristaltic pump. 35) Theapparatus of claim 29 wherein the variable-throughput device is capableof pulsed, continuous, variable and/or automated and/or programmablefluid movement. 36) The apparatus of claim 1 wherein the apparatus iscapable of applying a negative pressure within the wound dressing of upto 50% atm. 37) The apparatus of claim 36 comprising at least one bodyin the flow path to, over and from the wound bed which has sufficientresilience against the pressure to allow any significant compression ordecompression of the fluid occur. 38) The apparatus of claim 1 whereinthe one or more pipes comprise a manifold which covers and contacts asignificant area of the wound bed with openings for delivering and/orreceive fluid directly to/from the wound bed over an extended area. 39)The apparatus of claim 1 wherein securing means are provided to securethe wound dressing to the site of the wound. 40) A conformable wounddressing comprising: a backing layer with a wound-facing face which iscapable of forming a relatively fluid-tight seal or closure over awound; at least one pipe which passes through and/or under thewound-facing face to allow irrigation and/or aspiration of the wound;the point at which the or each inlet pipe and the or each outlet pipepasses through and/or under the wound-facing face forming a relativelyfluid-tight seal or closure over the wound in use; characterised in thatthe wound dressing comprises means for applying stress to the wound bedand optionally tissue surrounding the wound. 41) The wound dressing ofclaim 40 provided in a bacteria-proof pouch. 42) A method of operationof an apparatus for aspirating, irrigating and/or cleansing a wound,said method comprising the steps of: a) providing the apparatus of claim1; b) applying the wound dressing to the wound; c) conforming thebacking layer of the wound dressing to the shape of the bodily part inwhich the wound is to form a relatively fluid tight seal or closure; d)activating at least one device for moving fluid through the wounddressing to the wound and/or from the wound to cause irrigant to moveirrigant to the wound; and e) activating means for applying stress tothe wound bed and optionally tissue surrounding the wound. 43) Themethod of claim 42 wherein step (e) comprises activating means to applyoptionally varying positive and/or negative pressure to the wound bed.44) The method of claim 42 wherein the wound dressing comprises an inletand an outlet pipe and step (d) comprises activating the at least onedevice of moving fluid through the wound dressing to move fluid throughthe at least one inlet (irrigant) and out of the at least one outletpipe (aspirate). 45) The method of claim 42 wherein the flow rate offluid to the dressing is in the range of 1 to 1500 ml/hr. 46) The methodclaim 42 wherein the flow rate of total fluid out of the dressing is inthe range of 1 to 2000 ml/hr. 47) The method of claim 42 wherein step(d) comprises activating simultaneous irrigation and aspiration of thewound. 48) The method of claim 42 wherein step (d) comprises activatingsequential irrigation and aspiration of the wound. 49) The method ofclaim 42 wherein the apparatus is run at a negative pressure of up to50% atm. 50) The method of claim 42 wherein the stress is appliedintermittently.